Initialize compute manager before loading driver.

The compute virt API uses the conductor API instance on the compute
manager.  Make sure the compute manager has been fully initialized
before loading the driver and passing it the virtapi instance.  This
prevents the possibility of the driver calling back into the compute
manager and using something not initialized yet, such as the conductor
API in the case of this bug.

This patch also moves initialization of a member variable up above
super(), where the rest of the initialization is.  There doesn't appear
to be a reason for needing to have it at the end.

Fix bug 1156490.

Change-Id: I19684f24d590201d135336107425c2be2f74c83e
Merge "Initialize compute manager before loading driver."