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/diffmanifests.py

@@ -18,10 +18,12 @@ from color import Coloring
 from command import PagedCommand
 from manifest_xml import XmlManifest
 
+
 class _Coloring(Coloring):
   def __init__(self, config):
     Coloring.__init__(self, config, "status")
 
+
 class Diffmanifests(PagedCommand):
   """ A command to see logs in projects represented by manifests