Remove dbapi calls from agent driver

This commit removes dbapi calls from the agent driver in favor
of using objects. It also cleans up the object code a bit, and
adds some test objects to ironic.tests.objects.utils.

Closes-Bug: 1351329
Change-Id: I0b29654d0010386a4a08279cd0228090f2f02a45
Merge "Remove dbapi calls from agent driver"