* plugin/hosts: create inline map in setup

The inline map wasn't create in the setup.go fuction leading to a crash,
which is masked by a recover (but leads to a SERVFAIL, and not logging
the request).

Various other simplifications.

host plugin could use some test that actually cover these edgecases.
Signed-off-by: Miek Gieben <miek@miek.nl>

* PR review changes
Signed-off-by: Miek Gieben <miek@miek.nl>