test: skip mmio_stale_data vuln

This does not mean the guest is vulnerable, just that we don't give
enough information to the guest to tell if it is vulnerable ot not. The
docs[1] say that

    'Vulnerable: Clear CPU buffers attempted, no microcode':

    The processor is vulnerable, but microcode is not updated. The
    mitigation is enabled on a best effort basis.

We may not want to pass-through the microcode to the guest, as that
could be leveraged by an attacker.

[1]: https://www.kernel.org/doc/html/next/admin-guide/hw-vuln/processor_mmio_stale_data.html

Signed-off-by: Pablo Barbáchano <pablob@amazon.com>

Author: pb8o

tests/integration_tests/security/test_vulnerabilities.py

@@ -240,7 +240,7 @@ def check_vulnerabilities_files_on_guest(microvm):
     """
     vuln_dir = "/sys/devices/system/cpu/vulnerabilities"
     ecode, stdout, stderr = microvm.ssh.execute_command(
-        f"grep -r Vulnerable {vuln_dir}"
+        f"grep -r Vulnerable {vuln_dir} | grep -v mmio_stale_data:"
     )
     assert ecode == 1, f"stdout:\n{stdout}\nstderr:\n{stderr}\n"