Refine the "Council lookup service unavailable" exception
Refine the "Council lookup service unavailable" exception

The exception "Council lookup service unavailable" is
thrown periodically when MapIt is unavailable, although this
actually covers three different error conditions.  This commit
generates a different exception message for each.

mysociety/fixmytransport,mysociety/fixmytransport,mysociety/fixmytransport,mysociety/fixmytransport,mysociety/fixmytransport,mysociety/fixmytransport