Uses finer grained locking so that each volume name gets its own lock
rather than only being protected by the global lock, which itself needs
to be unlocked during cetain operations (`create` especially`)
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
- Add unit tests to make sure the functionality is correct.
- Add FilterByDriver to allow filtering volumes by driver, for future
`volume ls` filtering and whatnot.
Signed-off-by: David Calavera <david.calavera@gmail.com>
