(PE-37114) benchmark: send independent queries (console, etc)

Add a "--querier [N:]CATEGORY" option that can be repeated, and will
repeatedly select a random query from the CATEGORY send it to the
configured pdb, and discard the result.  The querier will currently
wait for (rand-int 6) seconds between queries.

When N is given it behaves exactly as if "--querier CATEGORY" had been
specified N times.

The categories and queries are read from the
puppetlabs.puppetdb.sample.queries resource, i.e. they're in
resources/puppetlabs/puppetdb/sample/queries.edn.