Tests: Add a test for valid filters

Tests: Add a test for valid filters

This test validate that for a given filter the expected trace output is
conform to the expected filter behavior.

This test rely on the babelstats utility. With the help of this script,
we can verify that the expected minimum and maximum values on fields of
interest are within the expected ranges.

For example, given 100 iterations on a tracepoint with the field
'intfield', with values starting from 0 and incrementing on each
iteration, and the filter expression 'intfield < 4', we would expect
that the min-max range lie within [0,3].

Thus, if the babelstat computed range does not match the expected range,
this could potentially indicate failure in the filtering mechanism.

Signed-off-by: Christian Babeux <christian.babeux@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>