When driver is `local` an empty string is given to the debug message.
This patch removes the debug statement.
```
Dec 20 19:07:01 localhost.localdomain docker[19734]:
time="2015-12-20T19:07:01.872021857+01:00" level=debug msg="Registering
new volume reference: driver , name
c2291b964b4d7b1b51ec51d2ccfe2544f83fd23404709225a43743c5faadad55"
```
Signed-off-by: Antonio Murdaca <runcom@redhat.com>
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>
