Updated the valid states for provision requests

The provision task has a state named "provisioned" which is
not currently a valid state for its associated provision request.
As a result, after a provision task has finished provisioning a
VM, the task's status can no longer be bubbled up to its parent
provision request due to a validation error.

https://bugzilla.redhat.com/show_bug.cgi?id=1122123
Merge pull request #252 from dillaman/bz1122123-miq-provision-request-states

Updated the valid states for provision requests