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
Merge pull request #87 from vuntz/fix-role-add

Only give ResellerAdmin role to ceilometer after creation of user