utils: Fail on doctest.testmod failure.

Signed-off-by: Tim 'mithro' Ansell <me@mith.ro>

v2x/lib/argparse_extra.py

diff --git a/v2x/lib/argparse_extra.py b/v2x/lib/argparse_extra.py
index a2faa9f..6c86f4e 100644
--- a/v2x/lib/argparse_extra.py
+++ b/v2x/lib/argparse_extra.py
@@ -109,4 +109,6 @@
 
 if __name__ == "__main__":
     import doctest
-    doctest.testmod()
+    failure_count, test_count = doctest.testmod()
+    assert test_count > 0
+    assert failure_count == 0, "Doctests failed!"

v2x/lib/mux.py

diff --git a/v2x/lib/mux.py b/v2x/lib/mux.py
index 372db92..51122a1 100644
--- a/v2x/lib/mux.py
+++ b/v2x/lib/mux.py
@@ -223,4 +223,6 @@
 
 if __name__ == "__main__":
     import doctest
-    doctest.testmod()
+    failure_count, test_count = doctest.testmod()
+    assert test_count > 0
+    assert failure_count == 0, "Doctests failed!"