build/init: use systemd-udev for RHEL systems
base.install: install hpssacli under RHEL to start to replace hpacucli
init.common:
 - kill dhclient on each try
 - store the PID on a different place for each interface
 - let dhclient try on last resort instead of aborting
build/pxe: do not rename ifaces under RHEL
src/hpacucli.py: start to support hpasscli