improve puppet module 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 tests skeleton
Update readme
Add test skeleton
Upgrade APT module version to avoid provisioning bug.
Adds repository key
Add repo as an anchor to ensure order
Clean up error message
Add todo file
Adds puppet versions to tests on travis