Add configuration capabilities to core repositories Some of the configuration capabilities were not available for core repositories like `google` or `mavenCentral`. This change adds the ability to configure such repositories, including the content filtering aspect.
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.