skip the volumes mounted when deleting the volumes of container.
use Binds key in hostConfig to detect volumes mounted from external.
Merge pull request #2488 from viirya/fix_container_volumes_delete

Skip the volumes mounted when deleting the volumes of container.
Add CacheExtra field to container.Config.
Factor cache-probing logic out of buildfile.commit() and CmdRun().
Record added-tree sha256 in buildfile.CmdAdd, probe and use cache.
Implement caching for remote ADD commands. Closes #880.
Add self to AUTHORS.