Work around synchronization lock issues

Make the block on stage C only wait for 900 seconds (15 minutes) to
prevent indefinite blocking.

The issue comes if a VM is being received, and the current unflush is
cancelled for a flush. When this happens, this lock acquisition seems to
block for no obvious reason, and no other changes seem to affect it.
This is certainly some sort of locking bug within Kazoo but I can't
diagnose it as-is. Leave a TODO to look into this again in the future.

node-daemon/pvcnoded/objects/VMInstance.py

@@ -555,9 +555,16 @@ class VMInstance(object):
         time.sleep(0.5)
 
         self.logger.out('Acquiring lock for phase C', state='i', prefix='Domain {}'.format(self.domuuid))
-        lock.acquire()
+        try:
+            # Wait for only 900 seconds on this step since we don't do anything and it can fail
+            # if a flush or unflush is cancelled. 900 seconds should be plenty for real long
+            # migations while still avoiding an indefinite blocking here.
+            # TODO: Really dig into why
+            lock.acquire(timeout=900)
             # This is strictly a synchronizng step
             lock.release()
+        except Exception:
+            self.logger.out('Failed to acquire lock for phase C within 15 minutes, continuing', state='w', prefix='Domain {}'.format(self.domuuid))
 
         time.sleep(0.5)