automated/linux/gst-validate: Add support for ignore tests

There are some gst-validate tests that fails depending on the board
so add a way to use a file stored in a git repository to ignore the
result.

The gst-validate-launcher dosen't provide a command line option to
exclude certain tests by design depends on write your own testsuite.py
module so this is the better implementation for now.

Change-Id: I8e05de42892a58c1ccb344eb72932217de23921d
Signed-off-by: Aníbal Limón <anibal.limon@linaro.org>
2 files changed