added molecular default test szenario and configured travis-ci

[baloo42]

This PR adds a basic structure using molecular, docker and travis ci.

Some default checks are disabled to get a green build. We should fix:

• idempotency check
• lint warnings and harden config
• enable and honor ansible-lint
• add other systems like centos, opensuse etc.
• write more tests!

[zeitounator]

Hi @BaluX,

As you may have seen in #36 and #38, the maintenance of this repo has been discontinued.

As a consequence, and after waiting for a response of the authors and suggestions from other contributors, I decided to fork the repo to go on with maintenance. You can find the new repo there: https://github.com/ansible-ThoTeam/nexus3-oss

I already integrated this current pull request and build upon it to integrate groovy syntax checking and tests on centos7 in parallel to Ubuntu Xenial. You're more than welcome to join and contribute if you have time and other contributions to propose. I'm also looking for good willing people for code reviews, writing more tests, documenting, preparing new releases/merges. Drop me an email (link on my github profile page) if you wish to get involved.

Cheers.