Small python test cleanup

* Use more precise exception handling
* Don't print out the port number
Make python tests's environment reproducible

Use virtualenv and pip to make reproducible environments. Add a Makefile
for convenience. Now, we should only run tests with the sitepackages and
python from virtualenv. The Makefile should set this up for you
transporently, so you should still only need to ever run
`make test-boto`.
Update python test README with new instructions
Eliminate extra dep in python test makefile

Previously `pip install -r requirements.txt` was running every time.
This commit cleans up the Makefile to only run this dep if the
requirements.txt file has changed, or the env dir has gone away.
Update python test README configuration

`enforce_multipart_part_size` must be `false`
Merge pull request #542 from basho/feature/virtualenvize-python-tests-rebased

Feature/virtualenvize python tests rebased