Tests: add 'none' target system to the tox configuration
Tests: add 'none' target system to the tox configuration

You can use this to run the unit tests only and skip the functional
tests.

You can also use this to run the functional tests on a specific
Vagrant box using the FABTOOLS_TEST_BOX and FABTOOLS_TEST_PROVIDER
environment variables.

bitmonk/fabtools,pombredanne/fabtools,AMOSoft/fabtools,ronnix/fabtools,fabtools/fabtools,ahnjungho/fabtools,n0n0x/fabtools-python,wagigi/fabtools-python,prologic/fabtools,davidcaste/fabtools