improvement: make with_unicorn listen-binding fully configurable

Currently it was only possible to use a unix://-based socket or the predefined 127.0.0.1:9292. Now it's possible to provide whatever listen destination unicorn should bind to. For unix-sockets you now have to provide the full path, e.g. unix:///path/to/file. Adjusted tests accordingly.

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
change travis tests rbx-2.1.1 -> rbx-2

This removes testing of the slightly older 2.1.1 release which is currently failing in TravisCI. This is due to missing bundler, which is officially packages as of 2.2.5 but works with travis starting from 2.2.0 (it uses rvm context).

With this tests move to the most current rubinius build, which is 2.2.6 at the moment.

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>