Add user namespace (mapping) support to the Docker engine

Adds support for the daemon to handle user namespace maps as a
per-daemon setting.

Support for handling uid/gid mapping is added to the builder,
archive/unarchive packages and functions, all graphdrivers (except
Windows), and the test suite is updated to handle user namespace daemon
rootgraph changes.

Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)

daemon/daemon_test.go

@@ -509,7 +509,7 @@ func initDaemonForVolumesTest(tmp string) (*Daemon, error) {
 		volumes:    store.New(),
 	}
 
-	volumesDriver, err := local.New(tmp)
+	volumesDriver, err := local.New(tmp, 0, 0)
 	if err != nil {
 		return nil, err
 	}