Loop for 600 seconds rather than checking nova-bm

Instead of waiting 600 seconds to create a test node and then remove
it, switch to looping over registering a node for the same period of
time, saving one pointless call, and removing the check_service()
anti-pattern.

Change-Id: Icd1295d10b0d346de87194f6473c8940f724df6e
Merge "Loop for 600 seconds rather than checking nova-bm"