TestKit backend output goes to stdout/stderr (#624)

From there, TestKit can pick it up and write it into logfiles if desired.
neo4j-drivers/testkit#309

Author: robsdedude

testkit/backend.py

@@ -1,7 +1,8 @@
 import subprocess
+import sys
 
 if __name__ == "__main__":
-    err = open("/artifacts/backenderr.log", "w")
-    out = open("/artifacts/backendout.log", "w")
     subprocess.check_call(
-        ["python", "-m", "testkitbackend"], stdout=out, stderr=err)
+        ["python", "-m", "testkitbackend"],
+        stdout=sys.stdout, stderr=sys.stderr
+    )