Add additional config option "default_image_is_advanced"

In patch [1] we added new config option to configure "advanced" image
which we are using in some tests which require it and can't run using
default Cirros image.
Unfortunatelly this made life of some downstream users harder as they
have CI systems which don't use devstack and don't have easy way to
load another "advanced" image and use it for those tests.

So now this patch adds one ore config option "default_image_is_advanced"
which has boolean value and defaults to False.
If this is set to True, tests which require advanced image will not be
skipped and default image will be used for those tests.

[1] https://review.openstack.org/#/c/609762/16/neutron_tempest_plugin/config.py

Co-Authored-By: Slawek Kaplonski <skaplons@redhat.com>

Change-Id: Ic78ee64a9350863ff5bd4b4baa4b20770e1b9d47
diff --git a/neutron_tempest_plugin/config.py b/neutron_tempest_plugin/config.py
index df07042..05142d8 100644
--- a/neutron_tempest_plugin/config.py
+++ b/neutron_tempest_plugin/config.py
@@ -86,6 +86,13 @@
     # Options for special, "advanced" image like e.g. Ubuntu. Such image can be
     # used in tests which require some more advanced tool than available in
     # Cirros
+    cfg.BoolOpt('default_image_is_advanced',
+                default=False,
+                help='Default image is an image which supports features '
+                     'that Cirros does not, like Ubuntu or CentOS supporting '
+                     'advanced features. '
+                     'If this is set to True, "advanced_image_ref" option '
+                     'is not required to be set.'),
     cfg.StrOpt('advanced_image_ref',
                default=None,
                help='Valid advanced image uuid to be used in tests. '