Id generator is too expensive to use for such trivial purposes.
Also, this was using an API of id generator which should never have been
added.
Also, this was bogus on several accounts:
- if the tag as provided by caller (as seems to be supported), then
  newActiveProcess would have used an unrelated tag.
- if the alarm activity fails and gets re-run later, the wrong tag will
  also be used.
Instead, generate the tag with a random value.