Fix various things so the functional tests will work under python3:
- A hashlib.md5() can only be update()d with an encoded string in py3.
- There's no dict.iteritems(), change to dict.items() (which is already
an iterator).
- Open temp files with 'w+' mode rather than the default 'w+b' (as an
alternative to encoding all the write and expected-read payloads as
bytes).
- (This is a weird one) Explicitly raise SkipTest from unittest (rather
than unittest2, which is where cls.skipException landed). Not sure why
this is busted, but this moves the ball.
Change-Id: Ic9b2b47848a600e87a3674289ae7ae8c3e091fee
f1d742f32a