[rt46602] Ensure test output in systests.output is not mixed up

[rt46602] Ensure test output in systests.output is not mixed up

When running all the system tests, output from a test is sent to a
test.output file in the test directory.  These are combined in to
systests.output when the run finishes.

(cherry picked from commit 055e5be9fd7555e24449157bc78b8c0852f9b7d1)
(cherry picked from commit 50769a4a9e699b74b2a6fa2d5dc91ca54c99d9f3)
(cherry picked from commit 818ac05cfcd5a22c9f945ca63ee1ace13f6d8a72)