[Travis] Give more time to tests

Travis was regularly failing because the full test suite with coverage
takestoo much time.
Bitcoin has some optimisations in there which allows them to give less
time to the test part of the process. We don't so until we do, we have
to reserve more time. We will probably have to restart manually more
travis jobs but that's the only way to have them run to the end.

.travis.yml

@@ -64,7 +64,7 @@ script:
   - export CONTINUE=1
   - if [ $SECONDS -gt 1200 ]; then export CONTINUE=0; fi  # Likely the depends build took very long
   - if [ $CONTINUE = "1" ]; then set -o errexit; source .travis/test_06_script_a.sh; else set +o errexit; echo "$CACHE_ERR_MSG"; false; fi
-  - if [ $SECONDS -gt 2000 ]; then export CONTINUE=0; fi  # Likely the build took very long; The tests take about 1000s, so we should abort if we have less than 50*60-1000=2000s left
+  - if [ $SECONDS -gt 1500 ]; then export CONTINUE=0; fi  # Likely the build took very long; The tests take about 1000s, so we should abort if we have less than 50*60-1000=2000s left
   - if [ $CONTINUE = "1" ]; then set -o errexit; source .travis/test_06_script_b.sh; else set +o errexit; echo "$CACHE_ERR_MSG"; false; fi
 after_script:
   - echo $TRAVIS_COMMIT_RANGE