R1:0d5538672caa

Detect unsynchronizable repositories on multiple cluster hosts

Summary:
Ref T12613. Currently, the SVNTEST and HGTEST repositories are improperly configured on `secure`. These repositories use VCS systems which do not support synchronization, so they can not be served from cluster services with multiple hosts.

However, I've incorrectly configured them the same way as all the Git repositories, which support synchronization. This causes about 50% of requests to randomly fail (when they reach the wrong…