Output Busser debug information for `kitchen list --debug`.
[Breaking] Remove Chef Omnibus GEM_PATH inclusion in Busser GEM_PATH.

This fully isolates Busser and its runner plugins to a GEM_HOME and
GEM_PATH of `<busser_root_path>/gems`.
Back out of #121 due to changes in the data internals of Test Kitchen.

This may return in another form in the future, promise!