nova_sync_quotas: iterate over tenants with 0 VMs
nova_sync_quotas: iterate over tenants with 0 VMs

Prior to this commit, the nova_sync_quotas.py script was only iterating
over tenants who had VMs created.  However, it's possible that a tenant
has zero VMs, but has a messed up quota.  This patch iterates over all
the tenants, including those with zero VMs.

dreamhost/os-maintenance-tools,dreamhost/os-maintenance-tools,drwahl/os-maintenance-tools,fzylogic/os-maintenance-tools,fzylogic/os-maintenance-tools,fzylogic/os-maintenance-tools,drwahl/os-maintenance-tools,drwahl/os-maintenance-tools,dreamhost/os-maintenance-tools