[GTK] [CMake] run-webkit-tests should support the CMake build

https://bugs.webkit.org/show_bug.cgi?id=126503

Reviewed by Daniel Bates.

Update run-launcher and gtk.py to work properly when dealing with the CMake port.
run-webkit-tests does not need the --gtkcmake flag, but run-launcher does.

* Scripts/run-launcher: Work properly with the gtkcmake flag.
* Scripts/webkitpy/port/gtk.py:
(GtkPort._is_cmake_build): Added this helper which looks for the CMakeCache
file to detect a CMake build.
(GtkPort._built_executables_path): Added this helper to locate the built executable path.
(GtkPort._built_libraries_path): Added this helper to locate the built library path.
(GtkPort._port_flag_for_scripts): Use --gtkcmake when appropriate.
(GtkPort.setup_environ_for_server): The way CMake builds libraries differs from GTK+.
(GtkPort._path_to_driver): Use the new helper.
(GtkPort._path_to_image_diff): Use the new Helper.
(GtkPort._path_to_webcore_library): Use the new helper.
(GtkPort.build_webkit_command): Use --gtkcmake when appropriate.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@162585 268f45cc-cd09-0410-ab3c-d52691b4dbfc