tests: move testrunner import up

Testrunner is now impported as a package found in PYTHONPATH, so
import can be placed at the top of the script as usual.

tests/thread_basic/tests/01-run.py

@@ -7,6 +7,7 @@
 # directory for more details.
 
 import sys
+from testrunner import run
 
 
 def testfunc(child):
@@ -15,5 +16,4 @@ def testfunc(child):
 
 
 if __name__ == "__main__":
-    from testrunner import run
     sys.exit(run(testfunc))