Load extension 2 times fix load sequence issue

Some extensions such as volumes need to inherit servers, however
the extension load sequence can't be guaranted. If the servers
extension is loaded after volumes, the controller of volumes will
be None and lead to problem.

Change-Id: Iec1e759f5c1f570a6b0ac65fb357b4f15102499c
Closes-Bug: #1373238
Merge "Load extension 2 times fix load sequence issue"