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>

subcmds/cherry_pick.py

@@ -97,7 +97,7 @@ change id will be added.
 
   def _StripHeader(self, commit_msg):
     lines = commit_msg.splitlines()
-    return "\n".join(lines[lines.index("")+1:])
+    return "\n".join(lines[lines.index("") + 1:])
 
   def _Reformat(self, old_msg, sha1):
     new_msg = []