Plugin config can have Mounts without a 'Source' field. In such cases,
performing a 'plugin set' on the mount source will panic the daemon. Its
the same case for device paths as well. This detects the case and
returns error.
Signed-off-by: Anusha Ragunathan <anusha.ragunathan@docker.com>
Upstream-commit: 6572e27df7f3483cfed7a8294c1f6d9cf157809a
Component: engine