run-tests: report interrupted tests

When the test run is aborted, a message is printed for each interrupted test.
This is helpful when a test is hanging.

example failure message:
INTERRUPTED: /path/to/tests/test-example.t

The message can appear before or after the line with the number of tests

tests/run-tests.py

@@ -962,7 +962,11 b' def runone(options, test, count):'
 
     if options.time:
         starttime = time.time()
-    ret, out = runner(testpath, testtmp, options, replacements, env)
+    try:
+        ret, out = runner(testpath, testtmp, options, replacements, env)
+    except KeyboardInterrupt:
+        log('INTERRUPTED:', test)
+        raise
     if options.time:
         endtime = time.time()
         times.append((test, endtime - starttime))