Fix some conductor manager return values.

A couple of methods in the compute manager were returning a db model as
the result of an rpc.call().  Since db models all contain non-primitive
types, this will cause failures in the rpc layer.

Related to bp no-db-compute.

Change-Id: I6e4af99bd75e4a367bdc83b969ed4d8252f69ba2
Make pinging conductor a part of conductor API.

This patch moves the loop that pings the conductor over rpc until it
responds to be a part of the conductor API.  This will allow it to be
used elsewhere in the code as needed.

Part of bp no-db-compute.

Change-Id: Ie027adef4a3af3059b4ab586e927c93ae1a86fe9
Merge "Fix some conductor manager return values."
Merge "Make pinging conductor a part of conductor API."