Fix python3 issues with devstack
Fix python3 issues with devstack

use six.b() as write() params have changed:
https://docs.python.org/2/library/stdtypes.html#file.write
https://docs.python.org/3/library/os.html#os.write

Change-Id: I276809f26a7a6fe6cc05203dc44fe30128e6090c

noironetworks/neutron,mahak/neutron,huntxu/neutron,noironetworks/neutron,openstack/neutron,mahak/neutron,huntxu/neutron,eayunstack/neutron,openstack/neutron,eayunstack/neutron,mahak/neutron,openstack/neutron