`riak727` test should remove 1.4 app.config when done [JIRA: RIAK-3119]

[macintux]

The presence of the app.config file means Riak can't start after the test is run. This is fine for giddyup et al, but when doing local tests/experimentation can cause significant confusion (just ask me, @tburghart, or @fadushin_.

[macintux]

should also add a comment to the top of the file explaining where it came from