test: update compat options tests with server:exec

Before the change all tarantool.compat options' tests were running on
the same instance, and because luatest uses multiple threads, they could
interfere with compat configuration at the same time as other test
checks default behavior. This could cause such tests to flack.

Now all options' tests are being run in a separate instance via
server:exec().

Closes #8033

NO_DOC=test fix
NO_CHANGELOG=test fix