docker has a new storage driver

Linux only!
There is now overlay2 too, so our hcp script needs to check for overlay
and overlay2. Maybe even overlay3, or overlay120 sometimes in the
future.

scripts/hcp.linux

@@ -52,7 +52,7 @@ getViStoLoc() {
 	    fi
 	    echo $basedir/aufs/diff/$mount_dir;;
 	btrfs) echo $basedir/btrfs/subvolumes/$dockerid;;
-	overlay) docker inspect $dockerid | grep UpperDir | awk '{print $2}' | cut -d'"' -f2;;
+	overlay*) docker inspect $dockerid | grep UpperDir | awk '{print $2}' | cut -d'"' -f2;;
     esac
 }