Fix python 3.6 escape char warnings in strings
Fix python 3.6 escape char warnings in strings

In python 3.6, escape sequences that are not
recognized in string literals issue DeprecationWarnings.

Convert these to raw strings.

Change-Id: I0e2bff9cb45974b159aed6a63913a63b1956aa32

openstack-dev/hacking,openstack-dev/hacking