(PDB-1076) Make environment garbage collection ignore null values

If a factset, report or catalog is migrated from an earlier puppetdb
version or submitted with a earlier puppetdb-terminus version it has
NULL as environment_id. If any of them have a record with that PuppetDB
failed to garbage collect any environments at all as the subselect
returned a NULL value.

Switching from UNION ALL to just UNION speeds up the query dramatically
as the return value from the subselect is much smaller (doesn't contain
any duplicates).
Merge pull request #1184 from dalen/pdb-1076-environment-gc-query

(PDB-1076) Make environment garbage collection ignore null values
(maint) delete extraneous arguments to factsets endpoint

The factsets endpoint has some non-functioning url arguments copied from the facts
endpoint in error. This patch deletes them.
Merge pull request #1190 from wkalt/maint/stable/delete-extraneous-factsets-arguments

(maint) delete extraneous arguments to factsets endpoint
(PDB-137) Document firewall and selinux requirements for PuppetDB.