(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
Merge pull request #1147 from senior/ticket/master/pdb-1011-pdb-query-from-service

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