box: handle SIGBUS in flightrec

Flight recorder uses mmapped file for performance reasons. Unfortunately
if for some reason mapping is not possible we got SIGBUS on accessing
mmapped memory.

We already handle this issue on flight recorder start in [1]. But if we
got SIGBUS in the meanwhile we currently got a crash. Let's just panic.

[1] https://github.com/tarantool/tarantool-ee/commit/e68b84768f3ae76aa9f03d36dd6f0587b884e1bb

CE Part of https://github.com/tarantool/tarantool-ee/issues/198

NO_DOC=stub for EE part
NO_CHANGELOG=stub for EE part
NO_TEST=tested in EE part