In order to speed up tests, avoid saving an RDB (mostly notable on shutdown),
except for tests that explicitly test the RDB mechanism
In addition, use `shutdown-on-sigterm force` to prevetn shutdown from failing
in case the server is in the middle of the initial AOFRW
Also a a test that checks that the `shutdown-on-sigterm default` is to refuse
shutdown if there's an initial AOFRW
Co-authored-by: Guy Benoish <guy.benoish@redislabs.com>
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