Map the Phabricator credentials ID
Currently, Phabricator credentials are described by number.
This solution isn't the best for maintenance and doesn't allow secrets
replacement easily (what if we want to hunt the number 2 in the repo?).
This change provides a new pillar entry, zr_credentials, to map the IDs
to dictionary keys.
The Zemke-Rhyne execution module is updated to support keys expressions
(with . or : as separatator) in addition to numeric values.
The key dotted format has been selected to be stable, as the key would
also be a valid expression to fetch the secret in other stores, like Vault.
Test Plan: salt equatower zr.get_username nasqueron.cachet.mysql
Reviewed By: dereckson
Maniphest Tasks: T1425
Differential Revision: http://devcentral.nasqueron.org/D1738