Enable all in one build in openstack-infra

This commit implements changes in the all in one scripted build in order
to make it work within openstack-infra:

1) flush all iptables rules put into place by openstack-infra
2) permit root login to sshd

Change-Id: Ib7eba632034f276184bd58fe33e5cab7f1c63b76
Closes-Bug: 1399651