Move duplicated _get_node(s)_mac_addresses()

Move duplicated _get_node(s)_mac_addresses() from pxe and ssh drivers
to a common place.

Change-Id: I27d1df6d3b63f3421d59d14d2b5b9f2c874d6580
Updated from global requirements

Change-Id: I76cdfdb0693d041310ae6ff64dab6edb8b1a88c4
Factor hash ring management out of the conductor

This patch pulls some logic around querying and instantiating hash
rings out of the ConductorManager into a new HashRingManager.

Change-Id: I523cb77aae287c44f59b40783e54f6557bc924bc
Fix Node object version

The IronicObject base class recently changed 'version' to 'VERSION', but a
patch to Node landed after it using the old attribute.

Change-Id: Ife139ae16314f5ea7bef83f36351f79e525f688b
Merge "Move duplicated _get_node(s)_mac_addresses()"
Merge "Fix Node object version"
Merge "Factor hash ring management out of the conductor"
Merge "Updated from global requirements"