Merge #17420: travis: Rework CACHE_ERR_MSG

9999a79 travis: Rework CACHE_ERR_MSG (MarcoFalke)

Pull request description:

  This should fix the misconception that we can fix build problems in forked repos. See bitcoin/bitcoin#17418 (comment)

Top commit has no ACKs.

Tree-SHA512: e0c86f6613fa38f4d4984420fa1fdc999829407c71024c3b92fd1d35afa98f4b5073af72656c83f607d5f6fab15f9ea629ca8be0b4e892c2fb65a226036c470a

Author: MarcoFalke

.travis.yml

@@ -48,7 +48,7 @@ env:
   global:
     - CI_RETRY_EXE="travis_retry"
     - CI_WAIT="while sleep 500; do echo .; done"
-    - CACHE_ERR_MSG="Error! Initial build successful, but not enough time remains to run later build stages and tests. Please manually re-run this job by using the travis restart button or asking a bitcoin maintainer to restart. The next run should not time out because the build cache has been saved."
+    - CACHE_ERR_MSG="Error! Initial build successful, but not enough time remains to run later build stages and tests. See https://docs.travis-ci.com/user/customizing-the-build#build-timeouts . Please manually re-run this job by using the travis restart button. The next run should not time out because the build cache has been saved."
 before_install:
   - set -o errexit; source ./ci/test/00_setup_env.sh
   - set -o errexit; source ./ci/test/03_before_install.sh