Add -prune option to dockerregistrySigned-off-by: Oleg Bulatov <obulatov@redhat.com> (commit: 7783364)
Extended test for registry garbage collectorSigned-off-by: Michal Minář <miminar@redhat.com> (commit: c9479ed)
Fix extended tests: Docker 17.03 is newer than 1.9Signed-off-by: Oleg Bulatov <obulatov@redhat.com> (commit: 5f7b63e)