Doc: Improved documentation about LVM overwrite behaviour
Doc: Improved documentation about LVM overwrite behaviour

LVM configuration is overwritten on nodes part of the hosts group.
This documentation explains that behaviour to a deployer, because
he may not think at first sight that its LVM configuration could
be overwritten in hosts others than the cinder ones.

Change-Id: I82769250f057bac28385cf63c8e1df7c7df511f5
Closes-Bug: #1488532

os-cloud/os-ansible-deployment,robb-romans/openstack-ansible,major/os-ansible-deployment,cloudnull/os-ansible-deployment,yanyao/newton,yanyao/openstack-ansible,yanyao/openstack-ansible,mancdaz/openstack-ansible,mrda/openstack-ansible,weezer/openstack-ansible,cfarquhar/openstack-ansible,stackforge/os-ansible-deployment,Logan2211/openstack-ansible,yanyao/newton,BjoernT/os-ansible-deployment,cfarquhar/openstack-ansible,mrda/openstack-ansible,major/openstack-ansible,major/os-ansible-deployment,openstack/openstack-ansible,BjoernT/openstack-ansible,weezer/openstack-ansible,mrda/openstack-ansible,BjoernT/os-ansible-deployment,os-cloud/os-ansible-deployment,stackforge/os-ansible-deployment,openstack/openstack-ansible,BjoernT/openstack-ansible,major/openstack-ansible,Logan2211/openstack-ansible,BjoernT/os-ansible-deployment,robb-romans/openstack-ansible,mancdaz/openstack-ansible,bunchc/openstack-ansible,bunchc/openstack-ansible,cloudnull/os-ansible-deployment