python: Style cleanup.

This patch does minor style cleanups to the code in the python and
tests directory.  There's other code floating around that could use
similar treatment, but updating it is not convenient at the moment.

python/ovs/process.py

@@ -15,13 +15,15 @@
 import os
 import signal
 
+
 def _signal_status_msg(type_, signr):
     s = "%s by signal %d" % (type_, signr)
     for name in signal.__dict__:
         if name.startswith("SIG") and getattr(signal, name) == signr:
             return "%s (%s)" % (s, name)
     return s
-    
+
+
 def status_msg(status):
     """Given 'status', which is a process status in the form reported by
     waitpid(2) and returned by process_status(), returns a string describing