Partial fix for bug 936

This is a partial fix for bug 936. It passes the OSM_VCA_CACERT variable into MON, to be used when initiating the legacy N2VC connection.

This required parameter was introduced by the work to use upstream libjuju.

Change-Id: Ief7fba168182f3a007d51464b3338693f6ff3755
Signed-off-by: Adam Israel <adam.israel@canonical.com>