devtools/internal/testutil: change service update order per Bogdan's suggestion.
devtools/internal/testutil: change service update order per Bogdan's suggestion.

The order is now:
All apps except for mounttable and device manager
device manager
wait for device mananger
mounttable
wait for mounttable
prod service check

Also moved logic of updating device manager's envelope into a separate function.

Change-Id: I6955cf10a3c15283caad1eceabc28e3bf794c5de

vanadium/go.jiri,vanadium/go.jiri