tests/qtest/fuzz-megasas-test: Add test for GitLab issue #521

tests/qtest/fuzz-megasas-test: Add test for GitLab issue #521

Without the previous commit, this test triggers:

  $ make check-qtest-x86_64
  [...]
  Running test qtest-x86_64/fuzz-megasas-test
  qemu-system-x86_64: softmmu/physmem.c:3229: address_space_unmap: Assertion `mr != NULL' failed.
  Broken pipe
  ERROR qtest-x86_64/fuzz-megasas-test - too few tests run (expected 2, got 1)

Suggested-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-Id: <20211119201141.532377-3-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>