TMF: Add functions to verify if events are present in a CTF Trace

TMF: Add functions to verify if events are present in a CTF Trace

These functions verify whether one, some or all events are present in the
metadata of a CTF trace.  It is useful to verify the presence of events
before doing an analysis that requires them.

Change-Id: Ieed7f9bcd905bf354aa5550b10c6304e534e5728
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/12952
Tested-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
IP-Clean: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
IP-Clean: Alexandre Montplaisir <alexmonthy@voxpopuli.im>