Fix flake8 complaints

mpcdf_branch.py

 #!/usr/bin/python2
 from __future__ import print_function
 
-import time
 import mpcdf_common
 
-import os
 import osc
 import osc.conf
 import osc.core
 import osc.cmdln
 
-from xml.etree import ElementTree
-
 
 def do_mpcdf_branch(self, subcmd, opts, *args):
     """${cmd_name}: Branch package from software to your home project