tmf: Introduce base class and extension point for on-demand analyses

tmf: Introduce base class and extension point for on-demand analyses

The on-demand analyses are analyses that are run manually when
the user requests it. As such, they are much more simple and
much less featureful than regular analyses.

The upcoming integration with the LTTng-Analyses scripts will
make use of this.

Change-Id: I012bcc3fe3ddbd586a8d23887a481d4bf927aadc
Signed-off-by: Alexandre Montplaisir <alexmonthy@efficios.com>
Reviewed-on: https://git.eclipse.org/r/70921
Reviewed-by: Hudson CI
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-by: Genevieve Bastien <gbastien+lttng@versatic.net>