Remove Travis CI config

Create Github Actions config
Split tox ini into one per supported distro so they can be run seperately

Signed-off-by: Adam Warner <me@adamwarner.co.uk>

test/tox.centos_8.ini

@@ -0,0 +1,8 @@
+[tox]
+envlist = py37
+
+[testenv]
+whitelist_externals = docker
+deps = -rrequirements.txt
+commands = docker build -f _centos_8.Dockerfile -t pytest_pihole:test_container ../
+           pytest {posargs:-vv -n auto} ./test_automated_install.py ./test_centos_fedora_common_support.py ./test_centos_common_support.py ./test_centos_8_support.py