* Fix host resolution on Darwin, use dig wherever possible
The `host` and `dig` commands do not return non-zero if a query returns NXDOMAIN
or NOERROR, but the DarwinHostProvider was expecting it when deciding whether to
fall back to IPv4 if a IPv6 query failed. Therefore, the `host` resource would
not function properly when resolving hostnames on Darwin. The logic has been
changed to use `dig` short output and query for both v6 and v4 addresses.
Additionally, the LinuxHostProvider has been modified to prefer `dig` if it's
available to keep behavior similar between Darwin and Linux whenever possible.
This has the added benefit of providing v6 and v4 resolution if possible where
`getent hosts` only returns v6 if v6 records exist.
Signed-off-by: Adam Leff <adam@leff.co>
