tmf: Add an XML trace stub with timestamps in seconds

tmf: Add an XML trace stub with timestamps in seconds

This trace takes exactly the same format as the original TmfXmlTraceStub, but
in this case, the timestamps are interpreted as seconds instead of nano.
This will allow to test analyses with various time units and make sure they
have the appropriate results.

Change-Id: I8cf90d39507cb0733872d8551e189b6ffa1103cc
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/88514
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>