Added autoinclude of archive::prerequisites and spec tests and smoke tests on Travis CI

I've added automatic auto include of archive::prerequisites but only if not given a custom one: https://github.com/wavesoftware/puppet-archive/commit/6fc35345eae76ad6479e707f50bc4568a1c897fe#diff-60ae41fd0a31977447947f59940ee9a4R61

I've also added rspec tests, and smoke tests for archive define. Both to be executed by Travis CI on 4 ruby/puppet configurations (1.8.7/2.7, 1.9.3/3.0, 2.0.0/3.0 and 2.1.0/3.7).

There are executed syntax checking for manifests, templates and libs, puppet-lint on manifests, rspec tests and smoke tests. Sample travis run: https://travis-ci.org/wavesoftware/puppet-archive/builds/37482860