"make test" fails in py3-only environment

[smithfarm]

Description of Issue/Question

On an openSUSE Leap 15.0 machine without Python 2 installed:

smithfarm@vanguard2:~/DeepSea> make test
sed "s/DEVVERSION/"0.9.6+142.g613db952"/" setup.py.in > setup.py
tox -e py27
GLOB sdist-make: /home/smithfarm/DeepSea/setup.py
py27 create: /home/smithfarm/DeepSea/.tox/py27
ERROR: InterpreterNotFound: python2.7
________________________________________________________ summary _________________________________________________________
ERROR:   py27: InterpreterNotFound: python2.7
make: *** [Makefile:967: test] Error 1

Expectation is that tox would use py3 in master branch.

[smithfarm]

@jschmid1 We cannot change this because Travis does not support Python 3?

I see that tox.ini does not have a [testenv:py3] section at all. . . .

[jschmid1]

our tests(and the libs we are relying on) are just not ported to py3. we have about 50~ tests failing when switching to python3