Update the patch not to use $TMPDIR, but to use an environment variable
dedicated for this purpose, because $TMPDIR has a different meaning.

With firefox 60, running `TMPDIR=/same/tmpdir/as/xvfb firefox --marionette` no
longer work and complains:

 Gtk-WARNING **: cannot open display: :0

If we investigate with strace we can see that marionette restarts with a
different $TMPDIR ( to store temporary files in another directory ) and we can see:

 connect(15, {sa_family=AF_UNIX, sun_path=@"/srv/slapgrid/slappart8/tmp/inst/TestRemoteDriver-0/tmp/Temp-0336e727-3485-4774-a816-75fda1baca12/.X11-unix"}, 113) = -1 EINVAL (Invalid argument)
 write(2, "\n(/srv/slapgrid/slappart8/tmp/soft/c5be5b0096cd286c70df5156590cf4f6/parts/firefox-60/firefox:29812): Gtk-\33[1;33mWARNING\33[0m **: cannot open display: :0\n", 152) = 152

To prevent this kind of problems, instead of using TMPDIR, use
a new dedicated environment variable XORG_LOCK_DIR.

No backward compatibility is provided, the profiles will be updated. In the
worst cases, non updated profiles will use /tmp/ and will work unless $DISPLAY
conflicts.