[test_operator] Add default for horizontest admin credentials

Recently, the defaults for the admin_password and admin_username
parameters were removed due to having out-of-date values. However,
the current state of the code is leaving them undefined, which
causes different errors. This PR aims to set the defaults to
empty string to fix both issues at once.

Signed-off-by: Katarina Strenkova <kstrenko@redhat.com>

Author: kstrenkova

roles/test_operator/defaults/main.yml

@@ -308,8 +308,8 @@ cifmw_test_operator_horizontest_config:
     storageClass: "{{ cifmw_test_operator_storage_class }}"
     privileged: "{{ cifmw_test_operator_privileged }}"
     containerImage: "{{ stage_vars_dict.cifmw_test_operator_horizontest_image }}:{{ stage_vars_dict.cifmw_test_operator_horizontest_image_tag }}"
-    adminUsername: "{{ stage_vars_dict.cifmw_test_operator_horizontest_admin_username }}"
-    adminPassword: "{{ stage_vars_dict.cifmw_test_operator_horizontest_admin_password | string }}"
+    adminUsername: "{{ stage_vars_dict.cifmw_test_operator_horizontest_admin_username | default('') }}"
+    adminPassword: "{{ stage_vars_dict.cifmw_test_operator_horizontest_admin_password | default('') | string }}"
     dashboardUrl: "{{ stage_vars_dict.cifmw_test_operator_horizontest_dashboard_url }}"
     authUrl: "{{ stage_vars_dict.cifmw_test_operator_horizontest_auth_url }}"
     repoUrl: "{{ stage_vars_dict.cifmw_test_operator_horizontest_repo_url }}"