test: Make CtfTmfTrace stubs of the right class

test: Make CtfTmfTrace stubs of the right class

Kernel and UST traces created with CtfTestTraceUtils were not of the
right type, which prevented the corresponding analyses to execute.

Add LttngKernelTestTraceUtils and LttngUstTestTraceUtils which create
similar stubs of the right type (LttngKernelTrace and LttngUstTrace).

Change-Id: I8a873b5ff7c558f68ffbc3141c66b8a35e6053c1
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/86297
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>