arm-auto-solutions/oeqa: Fix ptest-runner on EWAOL tests

During EWAOL tests (test_40_ewaol.py) the ptest-runner for
container-engine-integration-tests test is hitting the default
timeout of 300 seconds, increase the timeout by using its parameter.

While there, pass the special variable CE_TEST_IMAGE if MIRROR_DOCKER
is defined in the environment, so that the
container-engine-integration-tests will use a different docker
repository for the test, which will be defined by that variable.

Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>