Adds cleanup_files_locks() to nova/utils, which cleans up stale locks
left behind after process failures.
Adds a call to clean up locks on service startup for nova-api, nova-cert,
nova-compute, nova-network, nova-objectstore, and nova-scheduler.
Adds tools/clean_file_locks.py, which can be used to manually clean
stale locks.
Change-Id: I752e0b24d3c7fc5f1dc290da355cbd7f430789b8