MFH: r409108 devel/buildbot: Modernize (Ports compliance)

• Switch to new method of depending on Twisted, USES=twisted is DEPRECATED.
• Update and add TEST_DEPENDS, update test target
• Remove TESTS option
• Correctly limit Python version to -2.7
• Enable architecture independence (NO_ARCH)

Approved by: ports-secteam (miwi)