dns/py-py3dns: Limit to Python 3.x, Fix dependencies

py-py3dns is a Python 3.x only package, so limit USES=python
accordingly. ipaddr is needed on <= 3.2, so add it as a conditional
RUN_DEPENDS.

While I'm here:

• Add NO_ARCH
• Add test target, TEST_DEPENDS and patch outdated unit test assertions that test against live domains, not mocked responses.
• Remove unnecessary setup.py patch
• Match COMMENT to setup.py:description
• Sort and group USE{S} entries

PR: 206645
Reported by: danger
Approved by: portmgr (blanket)
MFH: 2016Q1
Differential Revision: D5083