Parses given argument and constructs new DNSPseudoURL
object. The format of the argument is: dns:[//host[:port]][/domain]
If no host information was given then localhost will be
used. If no port was given then the standard DNS server port
53 will be used. If no domain was given then the root
domain will be used. All domain here are treated as absolute domains.
Parameters: DNS - string representation of DNS URL throws: IllegalArgumentException - if the argument is not in acceptable format throws: NullPointerException - if the argument is null