Bug 1233: Accept vca argument in installer script

This fixes bug 1233 which caused the full_install_osm.sh
to not recognize the vca argument which is for the charmed
installation.

Bug: https://osm.etsi.org/bugzilla/show_bug.cgi?id=1233


Change-Id: Id5c653fa7ea543d946bdd7ae4fcdad3d431e9099
Signed-off-by: Dominik Fleischmann <dominik.fleischmann@canonical.com>