tests: stop pylint inferring the scientific stack

pylint parallelises per file, so the slowest file bounds the whole run.
tools/ab_plot.py took 15.4s of a 15.8s run, because astroid builds a
full AST for matplotlib, numpy, pandas, scipy and seaborn. Ignoring
them drops the check to 6.1s and reports the same messages: these
libraries resolve too dynamically for the member checks to fire.

Signed-off-by: Riccardo Mancini <mancio@amazon.com>