Update devstack section of quickstart to use agent_ipmitool
Update devstack section of quickstart to use agent_ipmitool

This patch updates the sample local.conf to use the agent_ipmitool
driver instead of the pxe_ssh driver. It also adds a note about *_ssh
drivers being phased out in favor of ipmitool + vbmc.

Change-Id: I1bc58b6b97f2aa0c864ebe112ca3c5a88b9ca561

SauloAislan/ironic,openstack/ironic,openstack/ironic,pshchelo/ironic,SauloAislan/ironic,NaohiroTamura/ironic,NaohiroTamura/ironic,pshchelo/ironic