git: fix status to use porcelain, ignore user configuration

From the git status doc:

    --porcelain

        Give the output in an easy-to-parse format for scripts. This is similar to the short output, but will remain stable across Git versions and regardless of user configuration. See below for details.

User configuration can break the git module from working as expected.

source_control/git.py

@@ -356,7 +356,7 @@ def has_local_mods(module, git_path, dest, bare):
     if bare:
         return False
 
-    cmd = "%s status -s" % (git_path)
+    cmd = "%s status --porcelain" % (git_path)
     rc, stdout, stderr = module.run_command(cmd, cwd=dest)
     lines = stdout.splitlines()
     lines = filter(lambda c: not re.search('^\\?\\?.*$', c), lines)