Revise troubleshooting text and compute steps

Revisded Troubleshooting.rst to help a user understand how to resolve
issues with compute nodes where OVS was not ready or completely
operational.  This is due to nova compute only relying upon the
existance of the bridge interface to determine if OVS flow is put
into place.  Bug filed: https://bugs.launchpad.net/nova/+bug/1391699

Additionally, updated the logic of the playbook to make it less
likely to encounter this issue by stopping nova-compute first, and
restarting the service last after pausing thirty seconds.

Change-Id: I432a3fc3f91f56ca81998a0487d72256c538c6af