Parse MiniSEED packets for INFO requests.

This enables reading INFO request responses from the IRIS ringserver.

(Previously the MiniSEED payload was simply guessed to start at 8 bytes
offset.)
Fixed use of builtin as variable name.
PEP8
Added unittest for different MiniSEED packets.
Added correct ticket number.
Python 3 compatibility
Flake8

(Sorry.)
Merge pull request #807 from bmorg/fix_seedlink_miniseed_parsing

Use clibmseed to parse INFO responses in MiniSEED