Remove shell scripts from tests

Specs were failing on windows when run under cmd.exe running the fixtures' shell script "tests". There was also a strange issue with the `pwd` command that is included with the omnibus package giving paths like `/usr/something`; using ruby instead fixes that problem as well.

The first commit is a refactor of the tests for the verify command, so it might be easier to look commit-by-commit on this one.

/cc @opscode/client-eng