[Contrib] Use global storage templates for PVC

[Contrib] Use global storage templates for PVC

OOM has now templates in order to create the needed PVC, using:

* a PV with a specific class when using a common nfs mount path between
nodes (sames as today use) --> is the default behavior today
* or a storage class if we want to use dynamic PV.
  On this case, we use (in order of priority):
  - persistence.storageClassOverride if set on the chart
  - global.persistence.storageClass if set globally
  - persistence.storageClass if set on the chart

Change-Id: I278e62821ca98e41f63306e502cca1019ba18756
Issue-ID: OOM-1227
Signed-off-by: Sylvain Desbureaux <sylvain.desbureaux@orange.com>