Don't resign raw version of the zone

Don't resign raw version of the zone

Update the function 'set_resigntime()' so that raw versions of
inline-signing zones are not scheduled to be resigned.

Also update the check in the same function for zone is dynamic, there
exists a function 'dns_zone_isdynamic()' that does a similar thing
and is more complete.

Also in 'zone_postload()' check whether the zone is not the raw
version of an inline-signing zone, preventing calculating the next
resign time.