Use GBN Broker for timesync if ERIC is disabled

bbmri/vars

@@ -14,7 +14,7 @@ do
 done
 
 SUPPORT_EMAIL=$ERIC_SUPPORT_EMAIL
-BROKER_URL_FOR_PREREQ=$ERIC_BROKER_URL
+BROKER_URL_FOR_PREREQ="{$ERIC_BROKER_URL:-$GBN_BROKER_URL}"
 
 if [ -n "$GBN_SUPPORT_EMAIL" ]; then
     SUPPORT_EMAIL=$GBN_SUPPORT_EMAIL
@@ -34,4 +34,4 @@ function do_enroll {
         echo
         echo "You just received $COUNT certificate signing requests (CSR). Please send $COUNT e-mails, with 1 CSR each, to the respective e-mail address."
     fi
-}
+}