Port syntax check rake tasks for GOV.UK repo

Syntax checks for Puppet manifests and templates. Adapted to use the
`exclude_paths` function from 59cf75f. Properly namespaced under `syntax:*`,
with an alias that calls both. Syntax comes before lint, in order or
importance.

Ideally these should be split out to a gem. Which will enable us to pull in
newer versions easily. For example, IDA have some much older copies of these
scripts which don't catch warnings, but now easy way to be notified of
updates or merge them in.

I've removed the `$stderr.puts` progress messages for the moment. There
might be a neater way to achieve those.