Use UID in systemd container name

enter.sh

@@ -13,8 +13,8 @@ fi
 # both).  Instead let's execute systemd-nspawn in a transient systemd
 # unit, then enter it using machinectl.
 
-UNIT=nilmbuntu-run-$VERSION
-MACH=nilmbuntu-$VERSION
+UNIT=nilmbuntu-run-$NONPRIV_UID-$VERSION
+MACH=nilmbuntu-$NONPRIV_UID-$VERSION
 
 setup_networking() {
     # We use a virtual ethernet adapter -- this requires that