Gem cleanup:

remove gemspec
don't gem install bundler, list it as dependency
add spec task to Rakefile and use that in travis
remove bundler/setup from hobson bin
remove unused gems: SystemTimer, childprocess, json, simplecov
Refactor workspace:

Use Open3 instead of popen4
Remove rvm init (it should inherit rvm/rbenv from calling environment)
Refactor way workspaces are prepared (no longer uses stash business)
Merge fork_and_execute functionality into execute
Use Open3 when fetching hostname. Open3 will call Process.detach, so the curl process cannot become a zombie.
Use new process group when executing commands so that they can be killed as one.
Add "jobs per test run" to Hobson config and add a default config
Bump to version 0.0.2