When $wgMainCache is CACHE_ANYTHING, recursion proceeds via
LoadBalancer::isPrimaryRunningReadOnly() until the DB server hits its
maximum connection limit. The try/catch blocks in ServiceWiring were no
longer effectively preventing this.
So, inspect the configuration to detect whether the main cache type will
be CACHE_DB, without actually instantiating it.
Bug: T334970
Change-Id: Ibdbc19c45eb20bb85df720669f7ce1d50e3656ff
dcb784311b