Give getAlmanacServiceURI() an "options" parameter to prepare for read-only devices

Summary:
Depends on D19355. Ref T10883. Ref T13120. Rather than adding a million parameters here, wrap the selector-parameters in an $options.

The next change adds a new "writable" option to support forcing selection of writable hosts.

Test Plan: Pulled and pushed via HTTP and SSH, viewed repositories via Diffusion.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13120, T10883

Differential Revision: https://secure.phabricator.com/D19356