Datacenter moid should not be tuple

Remove the comma, because it will convert the string to tuple
Closes-bug: #1362480

Change-Id: I2debb76bae26fe3d437a431f2946f66a1cbe6851
(cherry picked from commit ace3a01ebf980c166b4dfe6d1216b17bf0aec2ed)
Merge branch 'stable/icehouse' of https://github.com/openstack/quantum into stable/icehouse