add bashate (nee bash8) test support

style checks can now be run with 'tox'. This does not yet integrate
this to the gate, but it does clean up all the existing code to
work with the currently released bash8 pip.

Done as an easy example to create a pattern for other shell programs.

Change-Id: I5ecf28cfa2551f0cf3502263a379242c8803252c