perf: Fix scenario names that should not contain %

perf: Fix scenario names that should not contain %

The Scenario constructor in the o.e.test.performance contains this line of
code:

Assert.assertFalse(scenario.indexOf('%') >= 0);

This constructor does not appear to be called at insert, or it would fail, but
it is when reading the scenario data, which explains the performance tests job
failures when retrieving the data to display on
http://istmffastyet.dorsal.polymtl.ca.

Also changes the short names, that are limited to 40 characters in the database

Change-Id: If2a259e92595377a9a1872b008576a4564390038
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/69750
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>