Use the 'driver_lock' around read operations
Use the 'driver_lock' around read operations

To ensure that a file/group/folder is not being
removed while a read is underway (and therefore causing
corrupted msgpack reads) place the driver lock decorator
on the read methods to avoid this rare but possible
occurrence.

Change-Id: Ie2c53bd030aced77282cf575fd1024632e65348f

openstack/tooz,openstack/tooz