This test was essentially c/p-ed in 2cc3a7be3, consolidate

The overriding difference is the new-connection == new-storage == new-sqla
Add an explicit codepath to test that, but overall there is plenty of
other places that verify this behavior to death
Reaching for IO::File here makes no sense
Move the DSN-lock machinery from 8d6b1478d into DBICTest::BaseSchema

In the process adjust the RunMode loading order, and add a lib-wide frameskip
Generally this is just a c/p job, expecting zero functional changes