Fix logic for ipflush_onchange and restart_on_ipflush

Old logic for ipflush_onchange and restart_on_ipflush restored
for backward compatibility according readme and name semantics.

New pillar option introduced: ifdown_before_changes
New logic for PROD-22473 bug wraped in it
It should be disable in devcloud deployment due to
ifdown will not be executed correctly while interface configuration
is missing in /etc/network/interfaces, until configuration state happens

Related prod: PROD-28458 (PROD:28458)

Change-Id: Ib3263accde3d902fec98bd8676db29ff2812e7e2
1 file changed