There are 4 flavours of mutation source tests that are all ran
sequentially -- plain, reversed and upgrade/downgrade ones that
check v1<->v2 conversions.
This patch splits them all into individual calls so that some
tests may want to have dedicated cases for each. "By default" they
are all run as they were.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>