[Refactoring] In webkitpy/bindings/main.py, replace subprocess.Popen() with Executive

[Refactoring] In webkitpy/bindings/main.py, replace subprocess.Popen() with Executive
https://bugs.webkit.org/show_bug.cgi?id=73637

Reviewed by Adam Barth.

This patch replaces subprocess.Popen() with Executive, similar to other
Python scripts in webkitpy/. I manually confirmed that run-bindings-tests
works well for cases where no exception is raised, no exception is raised
but diff is found, and ScriptError is raised.

* Scripts/run-bindings-tests:
(main):
* Scripts/webkitpy/bindings/main.py: Replaces subprocess.Popen() with Executive.
(BindingsTests.__init__):
(BindingsTests.generate_from_idl):
(BindingsTests.generate_supplemental_dependency):
(BindingsTests.detect_changes):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@102105 268f45cc-cd09-0410-ab3c-d52691b4dbfc