ART: Add testrunner diagnostics for b/140161314

Try to give interpreter info on import failures.

Bug: 140161314
Test: art/test/testrunner/testrunner.py -b --host -t 001-Main
Test: manual (fake exception)
Change-Id: I9d8fd9b0dd115b2625cbf52eb1c96be70f7b4d09
diff --git a/test/testrunner/testrunner.py b/test/testrunner/testrunner.py
index 92d6241..e8b3655 100755
--- a/test/testrunner/testrunner.py
+++ b/test/testrunner/testrunner.py
@@ -46,7 +46,16 @@
 """
 import argparse
 import collections
-import concurrent.futures
+
+# b/140161314 diagnostics.
+try:
+  import concurrent.futures
+except Exception:
+  import sys
+  sys.stdout.write("\n\n" + sys.executable + " " + sys.version + "\n\n")
+  sys.stdout.flush()
+  raise
+
 import contextlib
 import datetime
 import fnmatch