YUM4/DNF compatibility via yum action plugin (#44322)

* YUM4/DNF compatibility via yum action plugin

DNF does not natively support allow_downgrade as an option, instead
that is always the default (not configurable by the administrator)
so it had to be implemented

 - Fixed group actions in check mode to report correct changed state
 - Better error handling for depsolve and transaction errors in DNF
 - Fixed group action idempotent transactions
 - Add use_backend to yum module/action plugin
 - Fix dnf handling of autoremove (didn't used to work nor had a
   default value specified, now does work and matches default
   behavior of yum)
 - Enable installroot tests for yum4(dnf) integration testing, dnf
   backend now supports that
 - Switch from zip to bc for certain package install/remove test
   cases in yum integration tests. The dnf depsolver downgrades
   python when you uninstall zip which alters the test environment
   and we have no control over that.
 - Add changelog fragment
 - Return a pkg_mgr fact if it was not previously set.

lib/ansible/plugins/action/yum.py

@@ -0,0 +1,100 @@
+# (c) 2018, Ansible Project
+#
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+from ansible.plugins.action import ActionBase
+
+try:
+    from __main__ import display
+except ImportError:
+    from ansible.utils.display import Display
+    display = Display()
+
+
+class ActionModule(ActionBase):
+
+    TRANSFERS_FILES = False
+
+    def run(self, tmp=None, task_vars=None):
+        '''
+        Action plugin handler for yum3 vs yum4(dnf) operations.
+
+        Enables the yum module to use yum3 and/or yum4. Yum4 is a yum
+        command-line compatibility layer on top of dnf. Since the Ansible
+        modules for yum(aka yum3) and dnf(aka yum4) call each of yum3 and yum4's
+        python APIs natively on the backend, we need to handle this here and
+        pass off to the correct Ansible module to execute on the remote system.
+        '''
+
+        self._supports_check_mode = True
+        self._supports_async = True
+
+        result = super(ActionModule, self).run(tmp, task_vars)
+        del tmp  # tmp no longer has any effect
+
+        # Carry-over concept from the package action plugin
+        module = self._task.args.get('use_backend', "auto")
+
+        if module == 'auto':
+            try:
+                if self._task.delegate_to:  # if we delegate, we should use delegated host's facts
+                    module = self._templar.template("{{hostvars['%s']['ansible_facts']['pkg_mgr']}}" % self._task.delegate_to)
+                else:
+                    module = self._templar.template("{{ansible_facts.pkg_mgr}}")
+            except Exception:
+                pass  # could not get it from template!
+
+        if module not in ["yum", "yum4", "dnf"]:
+            facts = self._execute_module(module_name="setup", module_args=dict(filter="ansible_pkg_mgr", gather_subset="!all"), task_vars=task_vars)
+            display.debug("Facts %s" % facts)
+            module = facts.get("ansible_facts", {}).get("ansible_pkg_mgr", "auto")
+            if (not self._task.delegate_to or self._task.delegate_facts) and module != 'auto':
+                result['ansible_facts'] = {'pkg_mgr': module}
+
+        if module != "auto":
+
+            if module == "yum4":
+                module = "dnf"
+
+            if module not in self._shared_loader_obj.module_loader:
+                result.update({'failed': True, 'msg': "Could not find a yum module backend for %s." % module})
+            else:
+                # run either the yum (yum3) or dnf (yum4) backend module
+                new_module_args = self._task.args.copy()
+                if 'use_backend' in new_module_args:
+                    del new_module_args['use_backend']
+
+                display.vvvv("Running %s as the backend for the yum action plugin" % module)
+                result.update(self._execute_module(module_name=module, module_args=new_module_args, task_vars=task_vars, wrap_async=self._task.async_val))
+                # Now fall through to cleanup
+        else:
+            result.update(
+                {
+                    'failed': True,
+                    'msg': ("Could not detect which major revision of yum is in use, which is required to determine module backend.",
+                            "You can manually specify use_backend to tell the module whether to use the yum (yum3) or dnf (yum4) backend})"),
+                }
+            )
+            # Now fall through to cleanup
+
+        # Cleanup
+        if not self._task.async_val:
+            # remove a temporary path we created
+            self._remove_tmp_path(self._connection._shell.tmpdir)
+
+        return result