Store forced connections in the Lisk connection cache

Summary:
In unit tests which use fixtures, we open transactions on every connection we establish. However, since we don't track connections that are established with "$force_new" (currently, only GlobalLock connections) we never close these transactions normally.

Instead of not tracking these connections, track them using unique keys so we'll never get a cache hit on them.

Test Plan: Built unit tests on top of this, had them stop dying from unclosed transactions.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1162

Differential Revision: https://secure.phabricator.com/D2938