Version bump to 2.1.5.
Fix two bug in ImageTests

The final assert didn't actually assert that the test
passed. The following expression pass

self.assertTrue('a' in x for x in ['b', 'c'])

This is because the expression creates a generator object
and doing ``bool`` on a generator object always return
True irrespective of it's values.
Don't retry failed requests that may spam Reddit

For instance, if a `submit` method call fails, then
it shouldn't be reattempted as the Reddit error may
occur after the new submission has been added to the
database. Meaning that the submission will be added
multiple times.
Deploy 2.1.6