Remove hard-coded DEPLOYWAIT timeout from Baremetal Scenario

Currently the baremetal scenario is hardcoded to wait 15 seconds
for the ironic node to reach the wait-callback state. This patch
adds a configuration option for this timeout and replaces the
hardcoded value with it.

Closes-Bug: #1526466

Change-Id: I8cded9467dc03d9e1a75222bb4b017604ae946af
2 files changed