Use --failfast when running functional tests on Travis

.travis.yml

@@ -80,7 +80,7 @@ script:
     - export LD_LIBRARY_PATH=$TRAVIS_BUILD_DIR/depends/$HOST/lib
     - if [ "$RUN_TESTS" = "true" ]; then travis_wait 50 make $MAKEJOBS check VERBOSE=1; fi
     - if [ "$TRAVIS_EVENT_TYPE" = "cron" ]; then extended="--extended --exclude feature_pruning,feature_dbcrash"; fi
-    - if [ "$RUN_TESTS" = "true" ]; then test/functional/test_runner.py --combinedlogslen=4000 --coverage --quiet ${extended}; fi
+    - if [ "$RUN_TESTS" = "true" ]; then test/functional/test_runner.py --combinedlogslen=4000 --coverage --quiet --failfast ${extended}; fi
 after_script:
     - echo $TRAVIS_COMMIT_RANGE
     - echo $TRAVIS_COMMIT_LOG