liberty版本devstack安装报错generate-subunit fail

各位朋友好：我在ubuntu14.04环境下安装liberty版本的devstack环境时，执行./stack/sh后
报错如下：
2017-05-08 06:38:40.129 | You are using pip version 7.1.2, however version 9.0.1 is available.
2017-05-08 06:38:40.130 | You should consider upgrading via the 'pip install --upgrade pip' command.
2017-05-08 06:38:40.151 | + exit_trap
2017-05-08 06:38:40.151 | + local r=1
2017-05-08 06:38:40.152 | ++ jobs -p
2017-05-08 06:38:40.152 | + jobs=
2017-05-08 06:38:40.152 | + [[ -n '' ]]
2017-05-08 06:38:40.152 | + kill_spinner
2017-05-08 06:38:40.152 | + '[' '!' -z '' ']'
2017-05-08 06:38:40.152 | + [[ 1 -ne 0 ]]
2017-05-08 06:38:40.152 | + echo 'Error on exit'
2017-05-08 06:38:40.152 | Error on exit
2017-05-08 06:38:40.152 | + generate-subunit 1494225476 44 fail
2017-05-08 06:38:40.203 | Traceback (most recent call last):
2017-05-08 06:38:40.203 | File "/usr/bin/generate-subunit", line 7, in
2017-05-08 06:38:40.203 | from os_testr.generate_subunit import main
2017-05-08 06:38:40.203 | File "/usr/lib/python2.7/site-packages/os_testr/__init__.py", line 19, in
2017-05-08 06:38:40.203 | 'os_testr').version_string()
2017-05-08 06:38:40.203 | File "/usr/lib/python2.7/site-packages/pbr/version.py", line 466, in version_string
2017-05-08 06:38:40.203 | return self.semantic_version().brief_string()
2017-05-08 06:38:40.203 | File "/usr/lib/python2.7/site-packages/pbr/version.py", line 461, in semantic_version
2017-05-08 06:38:40.203 | self._semantic = self._get_version_from_pkg_resources()
2017-05-08 06:38:40.203 | File "/usr/lib/python2.7/site-packages/pbr/version.py", line 438, in get_version_from_pkg_resources
2017-05-08 06:38:40.203 | import pkg_resources
2017-05-08 06:38:40.203 | File "/usr/lib/python2.7/site-packages/pkg_resources/_init__.py", line 72, in
2017-05-08 06:38:40.203 | import packaging.requirements
2017-05-08 06:38:40.203 | ImportError: No module named requirements
。
下面是我的local.conf配置文件

[[local|localrc]]
# Define images to be automatically downloaded during the DevStack built process.
IMAGE_URLS="http://download.cirros-cloud.net/0.3.4/cirros-0.3.4-x86_64-disk.img"
# Credentials
DATABASE_PASSWORD=123456
ADMIN_PASSWORD=123456
SERVICE_PASSWORD=123456
SERVICE_TOKEN=pass
RABBIT_PASSWORD=123456
#FLAT_INTERFACE=eth0

HOST_IP=192.168.192.130
SERVICE_HOST=192.168.192.130
MYSQL_HOST=192.168.192.130
RABBIT_HOST=192.168.192.130
GLANCE_HOSTPORT=192.168.192.130:9292

## Neutron options
Q_USE_SECGROUP=True
FLOATING_RANGE=192.168.192.0/24
FIXED_RANGE=10.0.0.0/24
Q_FLOATING_ALLOCATION_POOL=start=192.168.192.202,end=192.168.192.210
PUBLIC_NETWORK_GATEWAY=192.168.192.2
Q_L3_ENABLED=True
PUBLIC_INTERFACE=eth0
Q_USE_PROVIDERNET_FOR_PUBLIC=True
OVS_PHYSICAL_BRIDGE=br-ex
PUBLIC_BRIDGE=br-ex
OVS_BRIDGE_MAPPINGS=public:br-ex

# Work offline
#OFFLINE=True
# Reclone each time
RECLONE=False

# Logging
# -------
# By default ``stack.sh`` output only goes to the terminal where it runs. It can
# be configured to additionally log to a file by setting ``LOGFILE`` to the full
# path of the destination log file. A timestamp will be appended to the given name.
LOGFILE=/opt/stack/logs/stack.sh.log
VERBOSE=True
LOG_COLOR=True
SCREEN_LOGDIR=/opt/stack/logs

# the number of days by setting ``LOGDAYS``.
LOGDAYS=1
# Database Backend MySQL
enable_service mysql
# RPC Backend RabbitMQ
enable_service rabbit

# Enable Keystone - OpenStack Identity Service
enable_service key
# Horizon - OpenStack Dashboard Service
enable_service horizon
# Enable Swift - Object Storage Service without replication.
enable_service s-proxy s-object s-container s-account
SWIFT_HASH=66a3d6b56c1f479c8b4e70ab5c2000f5
SWIFT_REPLICAS=1
# Enable Glance - OpenStack Image service
enable_service g-api g-reg

# Enable Cinder - Block Storage service for OpenStack
VOLUME_GROUP="cinder-volumes"
enable_service cinder c-api c-vol c-sch c-bak
# Enable Heat (orchestration) Service
enable_service heat h-api h-api-cfn h-api-cw h-eng
# Enable Trove (database) Service
enable_service trove tr-api tr-tmgr tr-cond
# Enable Sahara (data_processing) Service
enable_service sahara

# Enable Tempest - The OpenStack Integration Test Suite
enable_service tempest

# Enabling Neutron (network) Service
disable_service n-net
enable_service q-svc
enable_service q-agt
enable_service q-dhcp
enable_service q-l3
enable_service q-meta
enable_service q-metering
enable_service neutron

## Neutron - Load Balancing
enable_service q-lbaas
## Neutron - Firewall as a Service
enable_service q-fwaas
## Neutron - VPN as a Service
enable_service q-vpn
# VLAN configuration.
#Q_PLUGIN=ml2
#ENABLE_TENANT_VLANS=True

# GRE tunnel configuration
#Q_PLUGIN=ml2
#ENABLE_TENANT_TUNNELS=True
# VXLAN tunnel configuration
Q_PLUGIN=ml2
Q_ML2_TENANT_NETWORK_TYPE=vxlan

# Enable Ceilometer - Metering Service (metering + alarming)
enable_service ceilometer-acompute ceilometer-acentral ceilometer-collector ceilometer-api
enable_service ceilometer-alarm-notify ceilometer-alarm-eval
enable_service ceilometer-anotification
## Enable NoVNC
enable_service n-novnc n-cauth

# Enable the Ceilometer devstack plugin
enable_plugin ceilometer https://git.openstack.org/openstack/ceilometer.git

# Branches
KEYSTONE_BRANCH=stable/liberty
NOVA_BRANCH=stable/liberty
NEUTRON_BRANCH=stable/liberty
SWIFT_BRANCH=stable/liberty
GLANCE_BRANCH=stable/liberty
CINDER_BRANCH=stable/liberty
HEAT_BRANCH=stable/liberty
TROVE_BRANCH=stable/liberty
HORIZON_BRANCH=stable/liberty
SAHARA_BRANCH=stable/liberty
CEILOMETER_BRANCH=stable/liberty
TROVE_BRANCH=stable/liberty

# Select Keystone's token format
# Choose from 'UUID', 'PKI', or 'PKIZ'
# INSERT THIS LINE...
KEYSTONE_TOKEN_FORMAT=${KEYSTONE_TOKEN_FORMAT:-UUID}
KEYSTONE_TOKEN_FORMAT=$(echo ${KEYSTONE_TOKEN_FORMAT} | tr '[:upper:]' '[:lower:]')

[[post-config|$NOVA_CONF]]
[DEFAULT]
# Ceilometer notification driver
instance_usage_audit=True
instance_usage_audit_period=hour
notify_on_state_change=vm_and_task_state
notification_driver=nova.openstack.common.notifier.rpc_notifier
notification_driver=ceilometer.compute.nova_notifier

请教各位朋友，十分感谢。