Minor fix to charmed installer. Expose OSM_HOSTNAME properly

Change-Id: I585eb7f490099fc9a86d072ab8e9a4b40ee378b9
Signed-off-by: David Garcia <david.garcia@canonical.com>

installers/charmed_install.sh

@@ -500,7 +500,7 @@ install_snaps
 bootstrap_k8s_lxd
 deploy_charmed_osm
 install_osmclient
-OSM_HOSTNAME=$(juju config nbi site_url | sed "s/http.*\?:\/\///"):443
+export OSM_HOSTNAME=$(juju config nbi site_url | sed "s/http.*\?:\/\///"):443
 add_local_k8scluster
 
 if [ -v MICROSTACK ]; then