At one instance (query_get_string_answer) it just flips the sign as it
is customary to return negative value upon error (for uniform
treatment).

Previously, running:

  touch /etc/booth/booth.conf
  booth grant a_ticket

would result in a segfault due to not guarding resolution of local
site properly in some circumstances, so do it at the central place.
Also error messaging is now centralized.

Respective logic was duplicated for all "booth list/peers/grant/revoke"
and "geostore list/get/set/del" separately, so utilize a natural control
flow to carry this once-resolved target site from here, sharing it with
the special case of "daemon" role invoked with "-s site" (debug mode).
Side effect: simpler, terser code.