Mapped IPv4 address test fix

The SubjectAlternativeNameTest was failing on getting a mapped IPv4
address back of the form "::ffff:127.0.0.1" which should be handled
fine.

Added several tests to InetAddressTest to make sure the correct handling
of mapped addresses doesn't regress.

Change-Id: If6e1ca8bda405d4862786404d1ced571743391f2