Remove obsolete mutter-test script

mutter-test was a script that was used to run various test on the
Metacity source tree (build with different options, etc.) This likely
hasn't been run once since the Metacity/Mutter branch point; remove
it to avoid confusion with the new test framework in src/tests.

https://bugzilla.gnome.org/show_bug.cgi?id=736505
Add meta_wayland_get_[x]wayland_display_name

Add private functions for the test framework to use to find out the
wayland and x11 display names, so they can set up the environment for
children.

https://bugzilla.gnome.org/show_bug.cgi?id=736505
Add meta_display_set_alarm_filter()

Add a private hook for the test framework to get XSyncAlarmEvent events -
this will be used to implement XSyncCounter based synchronization
so that the test framework can deterministically wait until Mutter
has seen actions performed by an X11 client.

https://bugzilla.gnome.org/show_bug.cgi?id=736505
Add meta_ui_window_is_dummy()

For reasons related to interaction between the GTK+ CSS code and the
frame sync protocol, the dummy GtkWindow that MetaUI creates to track
theme properties has to be mapped and have MetaWindow associated with it.
Add a private function so that the test framework can filter this out.

https://bugzilla.gnome.org/show_bug.cgi?id=736505
Add a test framework and stacking tests

Add a basic framework for tests of Mutter handling of client behavior;
mutter-test-runner is a Mutter-based compositor that forks off instances
of mutter-test-client and sends commands to them based on scripts.
The scripts also include assertions.

mutter-test-runner always runs in nested-Wayland mode since the separate
copy of Xwayland is helpful in giving a reliably clean X server to
test against.

Initially the commands and assertions are designed to test the stacking
behavior of Mutter, but the framework should be extensible to test other
parts of client behavior like focus.

The tests are installed according to:

https://wiki.gnome.org/Initiatives/GnomeGoals/InstalledTests

if --enable-installed-tests is passed to configure. You can run them
uninstalled with:

 cd src && make run-tests

(Not in 'make check' to avoid breaking 'make distcheck' if Mutter can't be
run nested.)

https://bugzilla.gnome.org/show_bug.cgi?id=736505