Support py34 tox target.

OpenStack is making a push to move projects that had been tested on py33
to py34 because py34 will have a much larger install base (and is
consequently easier to test).

The python 3.4 json lib returns new and different error strings when
json decoding fails. Remove assertions from test_load_list_from_json
hat check these error strings, instead simply rely on assertRaises to
assert that the appropriate error is thrown.

Change-Id: Ia6603783014b0114de0f29664834d21196744774