Description of problem:

Pre-flight storage checks do not go into enough detail with respect to custom partitioning.

https://github.com/openshift/openshift-ansible/blob/release-3.6/roles/openshift_health_checker/openshift_checks/disk_availability.py

The "etcd" node precheck looks for 20Gb of free space on /var.  In the case where /var represents multiple partitions, the check fails. For example: /var is 10Gb in size but as a separate partition, /var/lib/etcd is the required 20Gb in size.  

It should be possible to specify or check for a more specific directory/filesystem layout for required space.

Version-Release number of the following components:
[root@osemaster1 ~]$ rpm -q openshift-ansible
openshift-ansible-3.6.173.0.21-2.git.0.44a4038.el7.noarch

[root@osemaster1 ~]$ rpm -q ansible
ansible-2.2.3.0-1.el7.noarch

[root@osemaster1 ~]$ ansible --version
ansible 2.2.3.0
  config file = /etc/ansible/ansible.cfg
  configured module search path = Default w/o overrides
How reproducible:

Steps to Reproduce:
1. Have a mount point for a required directory, like /var/lib/etcd, with the correct recommended size
2. Have the top level that is checked, like /var, less than the recommended size
3. Run precheck

Actual results:

Precheck will fail on storage sizing

Expected results:

Should be able to account for or tolerate different layouts.

Additional info: