add another test to dns_list_base

to determine if the issue is with XML or multi
add a couple more tests, further testing.

these tests pass locally, but fail for Travis. Why?
define the array outside the call
dnsbl: replace forEach with async.each
dns_list_base: improved comments
update multi() call to skip tests for null zone
Merge pull request #746 from msimerson/dns_list_base

Dns list base