Move PORTAL Storage access to RWO

Move PORTAL Storage access to RWO

Today when deploying Portal with OOM, the PersistentVolumeClaim needs the
"ReadWriteMany" (or "RWX") capability.

According to Kubernetes Documentation (https://kubernetes.io/docs/concepts/storage/persistent-volumes/#access-modes),
ReadWriteMany stands for "the volume can be mounted as read-write by many nodes".

That means that a particular PVC needs to be read and written from many pods.
That also means that your code takes that into account and do the work to avoid
write at the same place at the same time.

An issue on RWX mode is that most "official" storage driver from Kubernetes doesn't
support it (13 over the 19 drivers doesn't support it, espacially OpenStack, Amazon
and Google storage classes).

Portal PVC are only used by a mariadb instance or a cassandra instance.
Thus we don't need RWX.

Change-Id: I706e13759d3af829d61d7a33d068263aaf9e9158
Issue-ID: PORTAL-724
Signed-off-by: Sylvain Desbureaux <sylvain.desbureaux@orange.com>