boot/ostree-remount.service: run before tmpfiles.d

tmpfiles.d configurations generally require write access to some places
that are read-only until ostree-remount runs.

Make sure ostree-remount has run first.

Thanks to Cosimo Cecchi for finding and diagnosing this problem.

https://bugzilla.gnome.org/show_bug.cgi?id=724183

src/boot/ostree-remount.service

@@ -26,6 +26,8 @@ After=systemd-remount-fs.service
 Before=local-fs.target umount.target
 # Other early boot units that need to write to /var
 Before=systemd-random-seed.service plymouth-read-write.service
+# tmpfiles.d usually needs write access to a few places
+Before=systemd-tmpfiles-setup.service
 
 [Service]
 Type=oneshot