Open the cache later to avoid scanning it twice if a connection is
made right away.

ClientStorage.close() is now idempotent.

ClientStorage stores its addr argument as self._addr so the test suite
doesn't have to dig it out of the rpc manager to reopen the storage as
readonly.

Renamed some of the callbacks into the client for clarity:
begin -> beginVerify
end -> endVerify
invalidate -> invalidateVerify
Invalidate -> invalidateTrans