[GTK] run-perf-tests should run the tests inside the jhbuild shell.
https://bugs.webkit.org/show_bug.cgi?id=133533

Patch by Carlos Alberto Lopez Perez <clopez@igalia.com> on 2014-06-05
Reviewed by Carlos Garcia Campos.

* Scripts/webkitpy/common/multiprocessing_bootstrap.py:
(run): Remove the jhbuild-wrapper wrapper from here. It should be
on Scripts/webkitpy/port/gtk.py.
* Scripts/webkitpy/port/base.py:
(Port.set_option): Add a set_option(name, value) function to set
the optparse parameter "name" to the value "value", even if the
parameter "name" is already initialized.
* Scripts/webkitpy/port/gtk.py:
(GtkPort.__init__): Set the default wrapper to jhbuild-wrapper.
If another wrapper is specified via the option "-l --wrapper=x",
then prepend the jhbuild-wrapper to the one specified.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@169614 268f45cc-cd09-0410-ab3c-d52691b4dbfc