devel/py-streamparse: update 3.14.0 to 3.15.0

• adopt port;
• contextlib2 added as dependency (based on what setup.py sets);
• texttable replaces prettytable (removed since 3.14.0 [348208b, #413]);
• sort RUN_DEPENDS;
• remove post-patch stage (it was removing test init script);
• add TEST_DEPENDS;
• check PYTHON_MAJOR_VER before adding extra dependencies (setup.py).

Approved by: araujo (mentor)
Differential Revision: https://reviews.freebsd.org/D18638