selftests: KVM: sev_migrate_tests: Add mirror command tests

Add tests to confirm mirror vms can only run correct subset of commands.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Marc Orr <marcorr@google.com>
Signed-off-by: Peter Gonda <pgonda@google.com>
Message-Id: <20211208191642.3792819-4-pgonda@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>