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/graphdriver/devmapper/devmapper_test.go

@@ -67,7 +67,7 @@ func testChangeLoopBackSize(t *testing.T, delta, expectDataSize, expectMetaDataS
 	d, err := Init(driver.home, []string{
 		fmt.Sprintf("dm.loopdatasize=%d", defaultDataLoopbackSize+delta),
 		fmt.Sprintf("dm.loopmetadatasize=%d", defaultMetaDataLoopbackSize+delta),
-	})
+	}, nil, nil)
 	if err != nil {
 		t.Fatalf("error creating devicemapper driver: %v", err)
 	}