Don't try to remove .repo if it doesn't exist

Part of the cleanup path for _Init is removing the .repo
directory. However, _Init can fail before creating the .repo directory,
so trying to remove it raises another exception:

    fatal: invalid branch name 'refs/changes/53/55053/4'
    Traceback (most recent call last):
      File "/home/mitchelh/bin/repo", line 775, in <module>
        main(sys.argv[1:])
      File "/home/mitchelh/bin/repo", line 749, in main
        os.rmdir(repodir)
    OSError: [Errno 2] No such file or directory: '.repo'

Fix this by only removing .repo if it actually exists.

Change-Id: Ia251d29e9c73e013eb296501d11c36263457e235

repo

@@ -114,6 +114,7 @@ import errno
 import optparse
 import os
 import re
+import shutil
 import stat
 import subprocess
 import sys
@@ -741,12 +742,7 @@ def main(orig_args):
       try:
         _Init(args)
       except CloneFailure:
-        for root, dirs, files in os.walk(repodir, topdown=False):
-          for name in files:
-            os.remove(os.path.join(root, name))
-          for name in dirs:
-            os.rmdir(os.path.join(root, name))
-        os.rmdir(repodir)
+        shutil.rmtree(repodir, ignore_errors=True)
         sys.exit(1)
       repo_main, rel_repo_dir = _FindRepo()
     else: