ctf: Add streamIntersection() method for CTF traces

ctf: Add streamIntersection() method for CTF traces

Stream intersection consists of trimming the trace to the time range
intersecting all CTF streams. This allows dropping events from areas
where only partial data is available.

This would be a good contender for re-using the trim() method. However
since trim() is currently implemented by calling Babeltrace, and
Babeltrace already has a stream intersection function, we can simply
call Babeltrace's function.

Change-Id: I9d38fbddccb2bee88aa4bca3f068efed24c295d5
Signed-off-by: Alexandre Montplaisir <alexmonthy@efficios.com>