Adding DynamicLoopingCall around lookup

Currently, if a single lookup call to the Ironic API fails, the entire
agent errors out and restarts. This allows the agent to retry for a set
amount of time before throwing an uncaught exception forcing a restart.

Change-Id: I39752fb3f42ad3e4f15a49194f1554e1d3463cf8
Closes-Bug: 1297019
Merge "Adding DynamicLoopingCall around lookup"