Azure CI: Update variable files instructions.

Update instuctions on Azure template varible files to reflect the
current test configuration behavior.

tests/azure/templates/variables_c8s.yaml

@@ -5,11 +5,13 @@
 #
 # Example:
 #
-# disabled_modules: >-
+# ipa_disabled_modules: >-
 #   dnsconfig,
 #   group,
 #   hostgroup
 #
+# If no variables are set, set "empty: true" as at least
+# one item is needed in the set.
 ---
 variables:
   empty: true

tests/azure/templates/variables_c9s.yaml

@@ -5,11 +5,13 @@
 #
 # Example:
 #
-# disabled_modules: >-
+# ipa_disabled_modules: >-
 #   dnsconfig,
 #   group,
 #   hostgroup
 #
+# If no variables are set, set "empty: true" as at least
+# one item is needed in the set.
 ---
 variables:
   empty: true

tests/azure/templates/variables_centos-7.yaml

@@ -5,11 +5,13 @@
 #
 # Example:
 #
-# disabled_modules: >-
+# ipa_disabled_modules: >-
 #   dnsconfig,
 #   group,
 #   hostgroup
 #
+# If no variables are set, set "empty: true" as at least
+# one item is needed in the set.
 ---
 variables:
   # ipa_enabled_modules: >-

tests/azure/templates/variables_fedora-latest.yaml

 #
+#
 # Variables must be defined as comma separated lists.
 # For easier management of items to enable/disable,
 # use one test/module on each line, followed by a comma.
 #
 # Example:
 #
-# disabled_modules: >-
+# ipa_disabled_modules: >-
 #   dnsconfig,
 #   group,
 #   hostgroup
 #
+# If no variables are set, set "empty: true" as at least
+# one item is needed in the set.
 ---
 variables:
   # ipa_enabled_modules: >-

tests/azure/templates/variables_fedora-rawhide.yaml

@@ -5,11 +5,13 @@
 #
 # Example:
 #
-# disabled_modules: >-
+# ipa_disabled_modules: >-
 #   dnsconfig,
 #   group,
 #   hostgroup
 #
+# If no variables are set, set "empty: true" as at least
+# one item is needed in the set.
 ---
 variables:
   empty: true