argparse was external in python 2.6 but not anymore, remove it from
requirements.
This should help with pip 8.0 that gets confused in this situation.
Installation of the external argparse is not needed.
Change-Id: Ib7e74912b36c1b5ccb514e31fac35efeff57378d
The configuration file parsers have a defined API, but we aren't
enforcing use of that. This adds an abstract base class that they
all will now inherit from. Additionally, new tests are added to
ensure the classes inherit from the new base class.
Moves tests for files in the config/ directory into their own
test directory.
Fixes the test class name for the ToxIni tests.
Change-Id: I003b4add6060075676da0f23cc37445ea50ffe88