SPEC-2996: rework the CAN modules tests

SPEC-2996: rework the CAN modules tests

The CAN modules tests have lots of redundant code, let's add some
function for probing/removing modules.

Furthermore, some tests cannot work with busybox ip, I adds some tests
for it.

When reworking the tests, I have removed the "lsmod |grep can" tests
which was of no value.
I have also removed all sleep which was undocumented(probably for some
log flushing), if something need them I will re-add it with comment.

Bug-AGL: SPEC-2996
Change-Id: I2e8a109d799c58726d848814fd4c21a9fbd2eef5
Signed-off-by: Corentin LABBE <clabbe@baylibre.com>