Fixes datastore selection bug

Currently the vmwareapi drivers will only select the first
available datastore it finds, even when there are other
datastores with capacity, it will fill one datastore completely
and then die.

Closes-bug: 1227825

Change-Id: I24f85114ea3f014950c27c0c91a6be352990d263
(cherry picked from commit 6c4b89a2ad51f92707acc01908b63bc507ad8fe7)