Add support for domain:hostAttr for nameservers

This enables support for nameservers returned as domain:hostAttr (for
example from EURid)
Wait for first 4 bytes of response

If a registrar is slow to reply (for example EURid) then the first 4
bytes of a response may not be immediately available. Therefore changed
to wait for all 4 bytes to be available before continuing.
Merge pull request #3 from catdevnull/master

EURid changes - domain:hostAttr & wait for response length