Bug 1579455 - [mozbuild] Fix some Python 3 incompatibilities in virtualenv.py r=nalexander

Differential Revision: https://phabricator.services.mozilla.com/D45072

--HG--
extra : moz-landing-system : lando

python/mozbuild/mozbuild/virtualenv.py

@@ -116,7 +116,8 @@ class VirtualenvManager(object):
         on OS X our python path may end up being a different or modified
         executable.
         """
-        ver = subprocess.check_output([python, '-c', 'import sys; print(sys.hexversion)']).rstrip()
+        ver = subprocess.check_output([python, '-c', 'import sys; print(sys.hexversion)'],
+                                      universal_newlines=True).rstrip()
         with open(self.exe_info_path, 'w') as fh:
             fh.write("%s\n" % ver)
             fh.write("%s\n" % os.path.getsize(python))
@@ -496,8 +497,8 @@ class VirtualenvManager(object):
         and call .ensure() and .activate() to make the virtualenv active.
         """
 
-        execfile(self.activate_path, dict(__file__=self.activate_path))
-        if isinstance(os.environ['PATH'], unicode):
+        exec(open(self.activate_path).read(), dict(__file__=self.activate_path))
+        if sys.version_info[0] < 3 and isinstance(os.environ['PATH'], unicode):
             os.environ['PATH'] = os.environ['PATH'].encode('utf-8')
 
     def install_pip_package(self, package, vendored=False):