Adding tests for the Splunk augeas rules

[chutzimir]

@jorritfolmer

As you commented at https://github.com/jorritfolmer/puppet-splunk/pull/60#issuecomment-1167698053 here is an attempt to add some test for the newly added Augeas rules. The tests are currently failing on Puppet 3 with

err: undefined method `_' for returns:Puppet::Type::Augeas::Returns

I don't know what to make of it, I was hoping you may have some insight.