Feature 10239: Distributed VCA

Add the following commands to the OSM Client:
 - osm vca-add
 - osm vca-delete
 - osm vca-update
 - osm vca-list
 - osm vca-show
Other changes:
 - Add the --vca argument in the osm vim-create command, to be able to
associate a vca with a VIM
Depends on: https://osm.etsi.org/gerrit/#/c/osm/NBI/+/10574/



Change-Id: I1d322745d16c5ade27444be5afd37904f7306c5c
Signed-off-by: David Garcia <david.garcia@canonical.com>