Fix raise_http_conflict_for_instance_invalid_state docstring

The docstring says it's returning an HTTPConflict exception but it's
actually raising one, there is no return value to the method. This can
also be implied from the method name, but the docstring should be
accurate.

Change-Id: I23f005db0342008f20dcbfe90e63a87339c98716
Merge "Fix raise_http_conflict_for_instance_invalid_state docstring"