Adds SNMP power driver
Adds SNMP power driver

Add a new PowerDriver module for remote control of node power by
enabling or disabling sockets on a rack power strip via SNMP.

Implements: blueprint ironic-snmp-power-driver
Change-Id: Ib16781eaa9737525c4d8a9231ecd9e72d7e2645e
Co-authored-by: David Hewson <00d704971e3cd2ae9db4a2c7fe913d128a395e25@cray.com>
Co-authored-by: Mark Goddard <e927bc1ff82b3a16b23dd278e89cdbcfc7d73604@cray.com>

NaohiroTamura/ironic-lib,openstack/ironic-lib,faizan-barmawer/ironic-lib,faizan-barmawer/elytics,citrix-openstack-build/ironic-lib