test: combine stdout/stderr from failed test

test: combine stdout/stderr from failed test

Printing stdout and stderr from a failed test makes it harder to
interpret what the specific problem was; instead let's print out
the lines in order as we got them when the test was run

Also save failed test output to file if ARTIFACT_DIRECTORY is defined

(cherry picked from commit d57e871c60805e3f1f57729ea8022477a611697d)