Bump hacking to 0.8

hacking 0.8 brings us bunch of python 3 compat rules.
Fix the python 3 compat issues to make this landable.

Change-Id: I0fbefefce92b506146e2bb833ffb0bd984b1c097
Partial-Bug: #1257301

keystoneclient/discover.py

@@ -357,7 +357,7 @@ class Discover(object):
             try:
                 v = self._get_factory_from_response_entry(version_data,
                                                           **client_kwargs)
-            except exceptions.DiscoveryFailure, e:
+            except exceptions.DiscoveryFailure as e:
                 _logger.warning("Invalid entry: %s", e, exc_info=True)
             else:
                 versions[v.version] = v

test-requirements.txt

@@ -1,4 +1,4 @@
-hacking>=0.5.6,<0.8
+hacking>=0.8.0,<0.9
 coverage>=3.6
 discover
 fixtures>=0.3.14