consistently set status as REBUILD when rebuilding

Consider an instance is in SHUTOFF status(stopped). When a rebuild
is issued on this instance, the status does not display as REBUILD.

Similarly, when a rebuild is issued on an instance and the operation
fails, the instance turns to ERROR state. Now if we issue a rebuild
again, the status does not display as REBUILD.

This patch fixes the above mentioned issues by displaying the correct
status i.e REBUILD.

Change-Id: Id11c9d31683a049c61fd751dc0ddabaf22c96cb9
Closes-Bug: #1362733
Merge "consistently set status as REBUILD when rebuilding"