[GTK] Test runner crashes without recent versions of pulseaudio-utils

[GTK] Test runner crashes without recent versions of pulseaudio-utils
https://bugs.webkit.org/show_bug.cgi?id=83774

Patch by Simon Pena <spena@igalia.com> on 2012-04-12
Reviewed by Philippe Normand.

Besides checking that pactl is available, check also that its output
is the expected one, and handle gracefully when it isn't, when
trying to unload pulseaudio modules.

* Scripts/webkitpy/layout_tests/port/gtk.py:
(GtkPort._unload_pulseaudio_module):
(GtkPort._restore_pulseaudio_module):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@113969 268f45cc-cd09-0410-ab3c-d52691b4dbfc