vca-config-access container for vnf/vdu configuration

This change implements the required changes in the IM
for features 1429 (secure key management) and 5669
(full charm support) so that OSM can know from the descriptor
whether or not the VNF/VDU requires SSH and what is the
default ssh user, so that OSM can inject an SSH public key
to make possible the configuration from VCA.

Change-Id: Ief9971a780f427c3d8de98d9d88fd0eae9493e5a
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>