pid1: add GracefulOptions= setting to .mount units

This new setting can be used to specify mount options that shall only be
added to the mount option string if the kernel supports them.

This shall be used for adding "usrquota" to tmp.mount without breaking compat,
but is generally be useful.

test/units/TEST-74-AUX-UTILS.mount.sh

@@ -185,3 +185,10 @@ systemctl status "$WORK_DIR/mnt"
 touch "$WORK_DIR/mnt/hello"
 [[ "$(stat -c "%U:%G" "$WORK_DIR/mnt/hello")" == "testuser:testuser" ]]
 systemd-umount LABEL=owner-vfat
+
+# Mkae sure that graceful mount options work
+GRACEFULTEST="/tmp/graceful/$RANDOM"
+systemd-mount --tmpfs -p GracefulOptions=idefinitelydontexist,nr_inodes=4711,idonexisteither "$GRACEFULTEST"
+findmnt -n -o options "$GRACEFULTEST"
+findmnt -n -o options "$GRACEFULTEST" | grep -q nr_inodes=4711
+umount "$GRACEFULTEST"