Remove ansible serial: option for haproxy and rabbitmq.
Remove ansible serial: option for haproxy and rabbitmq.

By having serial in site.yml for these roles will mean (particularly
during an upgrade) that tasks can be executed out of the intended
order across hosts, leading to unexpected results.

Change-Id: I44f0c66c445d853a2e4af69119562f13b4424936
Closes-Bug: #1626096

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