Add --relative cli argument for autoload layout testing in puppet-lint

[spacepants]

When validating a module via pdk validate, puppet-lint fails validation for its autoloader_layout check if the module directory is not the exact module name, i.e. if validating an ntp module, puppet-lint passes /path/ntp but fails /path/puppetlabs-ntp.

This passes the --relative argument to puppet-lint to ignore the top-most directory of the module and pass in both of the previous examples. Hopefully this should help with module conversion.

More info: rodjek/puppet-lint#245
and rodjek/puppet-lint#252

[coveralls]

Coverage remained the same at 92.295% when pulling d1cd252 on spacepants:relative-autoload-layout into c67927f on puppetlabs:master.

[bmjen]

I like this, thanks @spacepants !

I'll wait to merge this until the puppet-lint PRs are merged and released.