Make the puppetdb backend process primitive types for queries

cumin/backends/puppetdb.py: Modify grammar to recognize primitive
types, communicate quotedness to the final output as appropriate.

cumin/tests/unit/backends/test_puppetdb.py: Test several queries with
primitive types.

Bug: T207037
Change-Id: If83ce7f79a4f02d0e42f7d8b1e200b07181d8c17