optee-xtest.yml: clear storage before executing tests

Previously failed tests can leave some data in storage which
fails the tests later on unless data is cleared. --clear-storage
option is new to xtest:

OP-TEE/optee_test#670

See also:

https://gitlab.com/Linaro/trustedsubstrate/meta-ledge-secure/-/merge_requests/60

Ignore return values since the option may not exist in all xtest
versions and it can also report failures.

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>

automated/linux/optee/optee-xtest.yaml

@@ -25,5 +25,6 @@ params:
 run:
     steps:
         - cd ./automated/linux/optee/
+        - xtest --clear-storage || true
         - ./optee-xtest.sh -l "${TEST_LEVEL}" -t "${TEST_SUITE}" -s "${SE05X_TOOL}"
         - ../../utils/send-to-lava.sh ./output/result.txt