Check empty passwords in /etc/kolla/passwords.yml in prechecks
Check empty passwords in /etc/kolla/passwords.yml in prechecks

This patch set makes "kolla-ansible prechecks" flag an error if
any password is empty in /etc/kolla/passwords.yml.

Change-Id: I87dee25b79c97be64ca49a5638c7f5a30d4cf464
Closes-Bug: #1563506

mandre/kolla,dardelean/kolla-ansible,stackforge/kolla,rahulunair/kolla,mrangana/kolla,tonyli71/kolla,mandre/kolla,GalenMa/kolla,GalenMa/kolla,openstack/kolla,coolsvap/kolla,intel-onp/kolla,mrangana/kolla,mandre/kolla,dardelean/kolla-ansible,rahulunair/kolla,stackforge/kolla,tonyli71/kolla,coolsvap/kolla,nihilifer/kolla,nihilifer/kolla,coolsvap/kolla,intel-onp/kolla,dardelean/kolla-ansible,openstack/kolla,stackforge/kolla