Bug 1253359 - Vendor in Pytest 2.9.2 and Py 1.4.31 r=gps

Vendor in Pytest (2.9.2) and its requirement Py (1.4.31),
so that it can be used for e.g. the Marionette
harness unit tests and a pytest plugin for mozlog.

Copy pytest and py package directories (extracted from
tars on Pip) into `mozilla-central/python/`, removing
some support files (e.g. changelog, docs, tests).
Add both `.pth` entries to `virtualenv_packages.txt`.
Add both paths to `SEARCH_PATHS` in `mach_bootstrap.py`.

MozReview-Commit-ID: IOTCOUxX8R9

python/py/setup.py

@@ -0,0 +1,38 @@
+import os, sys
+
+from setuptools import setup
+
+def main():
+    setup(
+        name='py',
+        description='library with cross-python path, ini-parsing, io, code, log facilities',
+        long_description = open('README.txt').read(),
+        version='1.4.31',
+        url='http://pylib.readthedocs.org/',
+        license='MIT license',
+        platforms=['unix', 'linux', 'osx', 'cygwin', 'win32'],
+        author='holger krekel, Ronny Pfannschmidt, Benjamin Peterson and others',
+        author_email='pytest-dev@python.org',
+        classifiers=['Development Status :: 6 - Mature',
+                     'Intended Audience :: Developers',
+                     'License :: OSI Approved :: MIT License',
+                     'Operating System :: POSIX',
+                     'Operating System :: Microsoft :: Windows',
+                     'Operating System :: MacOS :: MacOS X',
+                     'Topic :: Software Development :: Testing',
+                     'Topic :: Software Development :: Libraries',
+                     'Topic :: Utilities',
+                     'Programming Language :: Python',
+                     'Programming Language :: Python :: 3'],
+        packages=['py',
+                  'py._code',
+                  'py._io',
+                  'py._log',
+                  'py._path',
+                  'py._process',
+        ],
+        zip_safe=False,
+    )
+
+if __name__ == '__main__':
+    main()