install ruby with helper

To use beaker needs shell executor.

The helper install PDK. And this permit to run all tests. But the output is strange with pdk through emulation console of the gitlabci.

So it should be possible to run tests also without pdk command. To do this the helper have to :

• at least install a ruby env management tool : rbenv.
• perhaps also install ruby and some gems like bundler.

Then it will be able to execute commands bundle exec rake beaker without pdk prefix.