Remove needless check

Starting `dockerd-rootless.sh` checks that `$HOME` is writeable, but does not
require it to be so.
Make the check more precise, and check that it actually exists and is a
directory.

Signed-off-by: Hugo Osvaldo Barrera <hugo@barrera.io>

contrib/dockerd-rootless.sh

@@ -28,8 +28,8 @@ if ! [ -w $XDG_RUNTIME_DIR ]; then
 	echo "XDG_RUNTIME_DIR needs to be set and writable"
 	exit 1
 fi
-if ! [ -w $HOME ]; then
-	echo "HOME needs to be set and writable"
+if ! [ -d $HOME ]; then
+	echo "HOME needs to be set and exist."
 	exit 1
 fi