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>

manifest_xml.py

@@ -56,6 +56,7 @@ urllib.parse.uses_netloc.extend([
     'sso',
     'rpc'])
 
+
 class _Default(object):
   """Project defaults within the manifest."""
 
@@ -74,6 +75,7 @@ class _Default(object):
   def __ne__(self, other):
     return self.__dict__ != other.__dict__
 
+
 class _XmlRemote(object):
   def __init__(self,
                name,
@@ -127,6 +129,7 @@ class _XmlRemote(object):
                       orig_name=self.name,
                       fetchUrl=self.fetchUrl)
 
+
 class XmlManifest(object):
   """manages the repo configuration file"""
 
@@ -655,7 +658,6 @@ class XmlManifest(object):
         if self._repo_hooks_project and (self._repo_hooks_project.name == name):
           self._repo_hooks_project = None
 
-
   def _AddMetaProjectMirror(self, m):
     name = None
     m_url = m.GetRemote(m.remote.name).url