Refactor Redstack to support install via devstack's local.sh hook

Right now we have 2 code paths for installation via devstack.
This trims down redstack so that we have only 1 code path (using the
local.sh hook) to install reddwarf via devstack.

Also added support to local.sh for setting the signing dir via
REDDWARF_AUTH_CACHE_DIR.

Fixes bug: 1154170
Fixes bug: 1105503

Change-Id: I12e61af2a6dd5e06cd59e8cd9947025f25d3dee6