Only give ResellerAdmin role to ceilometer after creation of user

We were doing it too early:

[Wed, 19 Feb 2014 00:11:50 +0000] INFO: Processing keystone_register[give ceilometer user ResellerAdmin role] action add_access (ceilometer::swift line 53)
[Wed, 19 Feb 2014 00:11:50 +0000] ERROR: Find /v2.0/tenants/c07ee0519edd45c087397534a2c4e690/users//roles: ResellerAdmin: Unknown response from Keystone Server
[Wed, 19 Feb 2014 00:11:50 +0000] ERROR: Response Code: 404
[Wed, 19 Feb 2014 00:11:50 +0000] ERROR: Response Message: Not Found

(cherry picked from commit 8d8c177aaf64c9fff512d06a333b6079e8a00bd2)
Merge pull request #88 from vuntz/fix-role-add-stoney

Only give ResellerAdmin role to ceilometer after creation of user