minor, provide -e|--existing-only for tzmap(1)'s cc command

This will instruct the tzmap compiler only to put zones
in the map file that currently (at the time of compilation)
exist on the system.
chore, use -e|--existing-only in .tzmap->.tzmcc recipe
test, adapt tzmap regression kicking the assumption that zones have to exist
Merge branch 'core/tzmaps'

* core/tzmaps:
  test, adapt tzmap regression kicking the assumption that zones have to exist
  chore, use -e|--existing-only in .tzmap->.tzmcc recipe
  minor, provide -e|--existing-only for tzmap(1)'s cc command