Add sequence test

Current tests do not cover sequence type in the babeltrace tests. This patch
adds an test that includes the sequence type.
Support for the sequence type

Add support for getting a sequence's valule in the python binding.
Add a sequence test in the python binding

This example is to test whether we can get a sequence's value in
the python binding well or not. It is used in conjunction with the
sequence test in the dir tests/ctf-traces/succeed/sequence.