Changes

ctrl: tweak errmsg for counter mismatch

- instead of "-1", print "not present", so humans know what is
  happening.
- the comma separated args in setverdict() create a lot of weird quotes.
  Use string concatenation to have only one set of quotes around the
  entire error message.

Related: OS#6545
Tweaked-by: Oliver Smith <osmith@sysmocom.de>
Change-Id: I672fcef819a6542a5b3bcfa0a6d9c84d34b468f3