命令还真没发现，不过可以修改配置文件实现。
实例的参数   quota_instances=10   就是在这里限制了只能在10个实例之内

这样我就能在配置文件中修改这个参数了
# vi /etc/nova/nova.conf
搜索到这个参数  把值改为15（根据自己的需求修改）   重启nova 服务


更多参数

Configuration option=Default value	(Type) Description
max_age=0	(IntOpt) number of seconds between subsequent usage refreshes
quota_cores=20	(IntOpt) number of instance cores allowed per project (tenant)
quota_driver=nova.quota.DbQuotaDriver	(StrOpt) Default driver to use for quota checks
quota_floating_ips=10	(IntOpt) number of floating ips allowed per project (tenant)
quota_gigabytes=1000	(IntOpt) number of volume gigabytes allowed per project (tenant)
quota_injected_file_content_bytes=10240	(IntOpt) number of bytes allowed per injected file
quota_injected_file_path_bytes=255	(IntOpt) number of bytes allowed per injected file path
quota_injected_files=5	(IntOpt) number of injected files allowed
quota_instances=10	(IntOpt) number of instances allowed per project (tenant)
quota_key_pairs=100	(IntOpt) number of key pairs allowed per user
quota_metadata_items=128	(IntOpt) number of metadata items allowed per instance
quota_ram=51200	(IntOpt) megabytes of instance ram allowed per project (tenant)
quota_security_group_rules=20	(IntOpt) number of security rules per security group
quota_security_groups=10	(IntOpt) number of security groups per project (tenant)
quota_volumes=10	(IntOpt) number of volumes allowed per project (tenant)
reservation_expire=86400	(IntOpt) number of seconds until a reservation expires
until_refresh=0	(IntOpt) count of reservations until usage is refreshed