deployment: execute ngcpcfg init-mgmt only if it's available

We don't have it on common PRO systems (like in our daily-build-pro),
so skip it if it's not available.

From: Michael Prokop <mprokop@sipwise.com>

deployment.sh

@@ -1315,7 +1315,11 @@ if "$PRO_EDITION" ; then
     ssh $PEER ngcpcfg pull
     ngcpcfg build
 
-    ngcpcfg init-mgmt $MANAGEMENT_IP
+    if ngcpcfg --help |grep -q init-mgmt ; then
+      ngcpcfg init-mgmt $MANAGEMENT_IP
+    else
+      echo "Skipping ngcpcfg init-mgmt as it is not available"
+    fi
   fi
 EOT
 fi