Use external repository mirrors in build (#6094) We've been bitten by external repository fluctuation for a long time. This PR makes most of tests use repository mirrors set up by ourselves via init script and system property.
There're still some tests not switching to mirrors, which would be fixed in follow-up commits.
JUnit 5 introduces @DisplayName and dynamic tests, which allows users to customize test case and test class' name. This should be taken into account. This PR introduces `displayName` and `classDisplayName` which are used for display. When rendering HTML reports, these two fields will be used.