Run validation steps prior to the matrix build

puppetlabs_spec_helper provides a task called validate which runs all
static checks (syntax, lint, etc). If these fail, there isn't really any
reason why you would want to start a full matrix build. Similarly, it
also runs Rubocop prior to the matrix. Otherwise you just get a full
failed matrix. The end result is less wasted CI on invalid syntax or
style.

This is taken from Voxpupuli's modulesync_config.

It also unifies on "validate lint check rubocop". This does depend on
puppetlabs_spec_helper version 2.16.0 or newer (which introduced the
common `check` task).