The sanity check replaces several old regression tests and provides a
quick test for checking mainly the readwritesplit routing behavior. It
also checks some of the connection counts and runs queries that once
caused a crash.
The set of tests that the sanity check obsoletes is:
bug422
bug469
bug448
bug507
bug509
bug634
bug694
bug669
bug711
mxs127
mxs47
mxs682_cyrillic
mxs957
mxs1786_statistics
rwsplit_read_only_trx
