don't try to resolve if WEBSERVER_IP is set and now use WEBSERVER_HOST.

don't try to resolve if WEBSERVER_IP is set and now use WEBSERVER_HOST.

as it crashed the installer when DNS doesn't respond as expected.

it will now use the WEBSERVER_HOST described in the doc but unused in the script.

TODO:

- lot of koha-httpd.conf generation is useless if you plan to use vhosts strategy
- on some recent linux distributions, $(getent hosts `hostname`) will give us
  127.0.0.1. this is to not mess up the MTA when there is no network. Don't
  you think there would be an error message in this case?
- default domain is localdomain .. this is not a good idea but i haven't a better one.
  can a network guru fix that ?

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>