Improve puppet module for thousandeyes agent installation

- te-agent.cfg file is not managed by an exec anymore which is not recommended.
- users can now install specific versions of the te-agent using $version parameter.
- init.pp is completely parameterized and variables are evaluated to avoid errors.
- Repositories are configured using the APT module which reduces complexity on the code.
- Configurations can be managed from hiera.
- Dependencies are more clear using $::lsbmajdistrelease facter variable.
- add boilerplate for rspecs