Add Secure Upgrade Test (sonic-net#6816)

What is the motivation for this PR?
We want to add a new secure upgrade test to validate non successful upgrade to non secure image.
In details:
If we have a secured image installed on a secured system, trying to install a non-secure image on it
should fail and we should expect a relevant message indicating so.

How did you verify/test it?
By taking a secured system with secured image installed on it and a path to non secure image we created privately,
we ran the test.

Supported testbed topology if it's a new test case?
Any topology is supported for the test.

Documentation
link to feature HLD: sonic-net/SONiC#1024

tests/platform_tests/test_secure_upgrade.py

@@ -0,0 +1,72 @@
+"""
+This test checks secure upgrade feature. If we have a secure system with secured image installed
+on it, the system is expected to install only secured images on it. So trying to install non-secure image
+will cause fail and a print of failure message to console indicating it is not a secured image.
+This test case validates the error flow mentioned above.
+
+In order to run this test, you need to specify the following argument:
+
+    --target_image_list (to contain one non-secure image path e.g. /tmp/images/my_non_secure_img.bin)
+
+Example run from tests directory:
+    "pytest platform_tests/test_secure_upgrade.py <regular arguments> --target_image_list non_secure_image.bin"
+"""
+import logging
+import pytest
+import re
+from tests.common.errors import RunAnsibleModuleFail
+from tests.common.helpers.assertions import pytest_assert
+from tests.upgrade_path.upgrade_helpers import install_sonic
+
+pytestmark = [
+    pytest.mark.topology('any'),
+    pytest.mark.disable_loganalyzer,
+]
+
+logger = logging.getLogger(__name__)
+
+
+@pytest.fixture(scope='function', autouse=True)
+def keep_same_version_installed(duthost):
+    '''
+    @summary: extract the current version installed as shown in the "show boot" output
+    and restore original image installed after the test run
+    :param duthost: device under test
+    '''
+    output = duthost.shell("show boot")['stdout']
+    results = re.findall(r"Current\s*\:\s*(.*)\n", output)
+    pytest_assert(len(results) > 0, "Current image is empty!")
+    current_version = results[0]
+    yield
+    duthost.shell("sudo sonic-installer set-default {}", format(current_version))
+
+
+@pytest.fixture(scope='session')
+def non_secure_image_path(request):
+    '''
+    @summary: will extract the non secure image path from --target_image_list parameter
+    :return: given non secure image path
+    '''
+    non_secure_img_path = request.config.getoption('target_image_list')
+    return str(non_secure_img_path)
+
+
+def test_non_secure_boot_upgrade_failure(duthost, non_secure_image_path, tbinfo):
+    """
+    @summary: This test case validates non successful upgrade of a given non secure image
+    """
+    # install non secure image
+    logger.info("install non secure image - expect fail, image path = {}".format(non_secure_image_path))
+    result = "image install failure"  # because we expect fail
+    try:
+        # in case of success result will take the target image name
+        result = install_sonic(duthost, non_secure_image_path, tbinfo)
+    except RunAnsibleModuleFail as err:
+        output_msg = str(err.results._check_key("module_stdout"))
+        err_msg = str(err.results._check_key("msg"))
+        logger.info("Expected fail, err msg is : {}\n\noutput_msg is {}".format(err_msg, output_msg))
+        pytest_assert(
+            "Failure: CMS signature verification failed" in str(output_msg),
+            "failure was not due to security limitations")
+    finally:
+        pytest_assert(result == "image install failure", "non-secure image was successfully installed")