Ceilometer may generate wrong format swift url in some situations

Ceilometer uses the admin URL registered in keystone to poll object store.
Usually the url is like: http://<host>:<port>, in some cases, user might
register the url like: http://<host>:<port>/v1
Ceilometer shall get the url registered in keystone and populate it to the
http://<host>:<port>/v1/AUTH_%(tenant_id)s style

Change the url population process the enhance the fault-tolerant capability
of Ceilometer

Change-Id: I3ec6ab0c330e35a2fd6bab36b8a2f43aee883b6d
Fixes: Bug 1183704
Merge "Ceilometer may generate wrong format swift url in some situations"