Add flake8 to the tidy process for Python files

Fixes #6236

Also included in this commit are the changes need to make flake8 pass
for the existing python file

python/servo/bootstrap_commands.py

@@ -40,7 +40,8 @@ def download(desc, src, dst):
         with open(dst, 'wb') as fd:
             while True:
                 chunk = resp.read(chunk_size)
-                if not chunk: break
+                if not chunk:
+                    break
                 recved += len(chunk)
                 if not dumb:
                     pct = recved * 100.0 / fsize
@@ -61,6 +62,7 @@ def download(desc, src, dst):
 
         sys.exit(1)
 
+
 def extract(src, dst, movedir=None):
     tarfile.open(src).extractall(dst)