Add test for python_venv language

testing/resources/python_venv_hooks_repo/.pre-commit-hooks.yaml

@@ -0,0 +1,5 @@
+-   id: foo
+    name: Foo
+    entry: foo
+    language: python_venv
+    files: \.py$

testing/resources/python_venv_hooks_repo/foo.py

@@ -0,0 +1,9 @@
+from __future__ import print_function
+
+import sys
+
+
+def main():
+    print(repr(sys.argv[1:]))
+    print('Hello World')
+    return 0

testing/resources/python_venv_hooks_repo/setup.py

@@ -0,0 +1,8 @@
+from setuptools import setup
+
+setup(
+    name='foo',
+    version='0.0.0',
+    py_modules=['foo'],
+    entry_points={'console_scripts': ['foo = foo:main']},
+)