Fix various whitespace issues reported by pyflakes

- E201 whitespace after '['
- E202 whitespace before '}'
- E221 multiple spaces before operator
- E222 multiple spaces after operator
- E225 missing whitespace around operator
- E226 missing whitespace around arithmetic operator
- E231 missing whitespace after ','
- E261 at least two spaces before inline comment
- E271 multiple spaces after keyword

Fixed automatically with autopep8:

  git ls-files | grep py$ | xargs autopep8 --in-place \
    --select E201,E202,E221,E222,E225,E226,E231,E261,E271

Change-Id: I367113eb8c847eb460532c7c2f8643f33040308c
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/254601
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: David Pursehouse <dpursehouse@collab.net>

git_refs.py

@@ -18,12 +18,12 @@ import os
 from repo_trace import Trace
 import platform_utils
 
-HEAD      = 'HEAD'
+HEAD = 'HEAD'
 R_CHANGES = 'refs/changes/'
-R_HEADS   = 'refs/heads/'
-R_TAGS    = 'refs/tags/'
-R_PUB     = 'refs/published/'
-R_M       = 'refs/remotes/m/'
+R_HEADS = 'refs/heads/'
+R_TAGS = 'refs/tags/'
+R_PUB = 'refs/published/'
+R_M = 'refs/remotes/m/'
 
 
 class GitRefs(object):