Introduce tag notation for checks

This allows us to refer to a group of checks using a single handle.

playbooks/byo/openshift-preflight/check.yml

@@ -9,6 +9,4 @@
     - action: openshift_health_check
       args:
         checks:
-          - package_availability
-          - package_update
-          - package_version
+          - '@preflight'

roles/openshift_health_checker/action_plugins/openshift_health_check.py

@@ -41,7 +41,7 @@ class ActionModule(ActionBase):
             return result
 
         args = self._task.args
-        requested_checks = set(args.get("checks", []))
+        requested_checks = resolve_checks(args.get("checks", []), known_checks.values())
 
         unknown_checks = requested_checks - set(known_checks)
         if unknown_checks:
@@ -93,3 +93,24 @@ class ActionModule(ActionBase):
             known_checks[check_name] = cls(module_executor=self._execute_module)
 
         return known_checks
+
+
+def resolve_checks(names, all_checks):
+    """Returns a set of resolved check names.
+
+    Resolving a check name involves expanding tag references (e.g., '@tag') with
+    all the checks that contain the given tag.
+
+    names should be a sequence of strings.
+
+    all_checks should be a sequence of check classes/instances.
+    """
+    resolved = set()
+    for name in names:
+        if name.startswith("@"):
+            for check in all_checks:
+                if name[1:] in check.tags:
+                    resolved.add(check.name)
+        else:
+            resolved.add(name)
+    return resolved

roles/openshift_health_checker/openshift_checks/__init__.py

@@ -26,6 +26,15 @@ class OpenShiftCheck(object):
         """The name of this check, usually derived from the class name."""
         return "openshift_check"
 
+    @property
+    def tags(self):
+        """A list of tags that this check satisfy.
+
+        Tags are used to reference multiple checks with a single '@tagname'
+        special check name.
+        """
+        return []
+
     @classmethod
     def is_active(cls, task_vars):  # pylint: disable=unused-argument
         """Returns true if this check applies to the ansible-playbook run."""

roles/openshift_health_checker/openshift_checks/package_availability.py

@@ -7,6 +7,7 @@ class PackageAvailability(NotContainerized, OpenShiftCheck):
     """Check that required RPM packages are available."""
 
     name = "package_availability"
+    tags = ["preflight"]
 
     def run(self, tmp, task_vars):
         try:

roles/openshift_health_checker/openshift_checks/package_update.py

@@ -7,6 +7,7 @@ class PackageUpdate(NotContainerized, OpenShiftCheck):
     """Check that there are no conflicts in RPM packages."""
 
     name = "package_update"
+    tags = ["preflight"]
 
     def run(self, tmp, task_vars):
         args = {"packages": []}

roles/openshift_health_checker/openshift_checks/package_version.py

@@ -7,6 +7,7 @@ class PackageVersion(NotContainerized, OpenShiftCheck):
     """Check that available RPM packages match the required versions."""
 
     name = "package_version"
+    tags = ["preflight"]
 
     @classmethod
     def is_active(cls, task_vars):