Sprinkle raw strings across the code base

tox / pytest is complaining about lots and lots of invalid escape
sequences in our code base. Sprinkle raw strings or backslash escapes
across the code base to fix most occurences of:

  DeprecationWarning: invalid escape sequence

There is still one warning that keeps repeating, though:

  source:264: DeprecationWarning: invalid escape sequence \d

Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>

ipapython/kerberos.py

@@ -109,7 +109,7 @@ class Principal(object):
         return hash(self.components + (self.realm,))
 
     def _parse_from_text(self, principal, realm=None):
-        """
+        r"""
         parse individual principal name components from the string
         representation of the principal. This is done in three steps:
             1.) split the string at the unescaped '@'