(PDB-1011) Allow querying of PDB directly via a TK service

This commit adds a function to the PuppetDBServer service to execute a
query and return the results as a Clojure data structure (rather than
streaming JSON over HTTP). A function can be passed in that will accept
a lazy seq to consume the rows
I thought all of the stuff that used the query engine went through this case statement. Is that not true?