Fix blank line issues reported by flake8

- E301 expected 1 blank line
- E302 expected 2 blank lines
- E303 too many blank lines
- E305 expected 2 blank lines after class or function definition
- E306 expected 1 blank line before a nested definition

Fixed automatically with autopep8:

  git ls-files | grep py$ | xargs autopep8 --in-place \
    --select E301,E302,E303,E305,E306

Manually fix issues in project.py caused by misuse of block comments.

Change-Id: Iee840fcaff48aae504ddac9c3e76d2acd484f6a9
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/254599
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: David Pursehouse <dpursehouse@collab.net>

subcmds/selfupdate.py

@@ -22,6 +22,7 @@ from command import Command, MirrorSafeCommand
 from subcmds.sync import _PostRepoUpgrade
 from subcmds.sync import _PostRepoFetch
 
+
 class Selfupdate(Command, MirrorSafeCommand):
   common = False
   helpSummary = "Update repo to the latest version"