Update application tests to run under Python 3

[zenmonkeykstop]

The configuration tests under '/tests' are written for Python2.
On dom0, compare the results of

make test

and

python3 -m unittest discover tests

The tests should be updated to run under Python3, and the Makefile targets should use Python3 explicitly.

[conorsch]

Took a look at this while builds were running; the diff is quite small to update the config tests (as usual, update string handling to use .decode("utf-8") where appropriate). Will submit as part of another PR later today.