Code review comment for lp:~nskaggs/juju-ci-tools/add-sane-args-defaults

The general idea of having sane defaults for the positional arguments I'm down with, I think we could even default 'env' to 'lxd' or something.

Given this changes add_basic_testing_arguments, TestAddBasicTestingArguments should be changed.

$ rm -rf /tmp/logs
$ touch /tmp/logs
$ make test
...
FAILED (failures=2, errors=37)

Some other comments inline.