turris-utils: modify script to also provide result INCONCLUSIVE

There are cases when there is no ip address of gateway available or when it is just hard to parse it. In that case we instead of trying to be smart report INCONCLUSIVE.

This also removes dependency checks between gateway and external IPs check and DNS check. This is done because we can't say that networks isn't working if for example gateway does not respond to ping. That can be just working network configuration.

Fixes https://gitlab.labs.nic.cz/turris/turris-os-packages/issues/456