Mknod more loopbacks for devmapper

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Upstream-commit: f8509e7940d73ecc0071faf15a865acb1f8dad52
Component: engine

components/engine/daemon/graphdriver/devmapper/devmapper_test.go

@@ -13,6 +13,9 @@ func init() {
 	DefaultDataLoopbackSize = 300 * 1024 * 1024
 	DefaultMetaDataLoopbackSize = 200 * 1024 * 1024
 	DefaultBaseFsSize = 300 * 1024 * 1024
+	if err := graphtest.InitLoopbacks(); err != nil {
+		panic(err)
+	}
 }
 
 // This avoids creating a new driver for each test if all tests are run