pkg/mount: MakeMount: minor optimization

Current code in MakeMount parses /proc/self/mountinfo twice:
first in call to Mounted(), then in call to Mount(). Use
ForceMount() to eliminate such double parsing.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

pkg/mount/sharedsubtree_linux.go

@@ -59,7 +59,7 @@ func MakeMount(mnt string) error {
 		return nil
 	}
 
-	return Mount(mnt, mnt, "none", "bind")
+	return ForceMount(mnt, mnt, "none", "bind")
 }
 
 func ensureMountedAs(mountPoint, options string) error {