[Common] Use global storage templates for PVC

[Common] 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

I've also aligned the PV creation of the different charts.
I've also aligned the PVC creation of the different charts.

I've removed unused mysql chart and (badly) used nfs-provisioner chart.

I've also make cassandra backup work with dynamic PV (but RWX only for
now).

Change-Id: I0ea3f8c7514ca648d94b6c682684c06b822bbe0a
Issue-ID: OOM-2229
Issue-ID: OOM-2228
Issue-ID: OOM-2227
Issue-ID: OOM-1227
Signed-off-by: Sylvain Desbureaux <sylvain.desbureaux@orange.com>