Correct errors introduced by using latest apt module

Since librarian-puppet had locked to old versions of Forge modules
but puppetlabs_spec_helper is now pulling the latest version,
there's this incompatibility to take care of in the test suite.
Extend Travis test matrix

* Add ruby 2.1.0
* Add back ruby 1.8.7 as allowed failure - shows test results
  but won't mark build as failed
* Enable fast finish - quick feedback on failed builds
* Make test matrix explicit so it's easier to tell what's included
  in the matrix, instead of excluding certain combinations
Add validate and lint tasks to travis script
Disable noisy/unneeded puppet-lint checks

* disable '80 characters check' - this is pretty useless and noisy
* disable 'class inherits from params class' check - is for puppet 2.6 which isn't supported
* disable 'only variable string check' - currently required by puppetlabs-concat
Fix remaining lint warnings
Fail on lint warnings from now on

Should improve PR quality and eliminate need for PRs to fix
any future lint issues