ctf: Fix lost events in a more elegant way

ctf: Fix lost events in a more elegant way

- Read the stream context packet once instead of at each load
  of the packet.
- Clean up code.
- Change the API to handle seeks to a specific event in a timestamp.
- Update test cases.

Change-Id: I0dddf56645bc0b8a69256ac947f3a806d1cfedf3
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/7075
Reviewed-by: Bernd Hufmann <bhufmann@gmail.com>
IP-Clean: Bernd Hufmann <bhufmann@gmail.com>
Tested-by: Bernd Hufmann <bhufmann@gmail.com>