Fixes #6147 - filter both org and env in sys

systems index action does not filter by environment_id when both
organization_id and environment_id are passed; it only filters by
organization_id. This allows the index action to filter by both.
fixes #6204 / BZ 1099016 - Fix gpg key on repo create and yum retrieval

This commit addresses 2 issues:
1. update the repo create to support associating the gpg key url
   in candlepin
2. update the v2 api to expose the 'gpg_key_content' api to enable
   yum clients to retrieve the key
Merge pull request #4244 from dustint-rh/system_index_filter_org_env

Fixes #6147 - filter both org and env in sys
Merge pull request #4263 from bbuckingham/issue-6204

fixes #6204 / BZ 1099016 - Fix gpg key on repo create and yum retrieval