virt_net: idempotency of create/stop actions (#53276)

Currently, if we try to stop or start a network two time in a row, the
second call will fail. With this patch:

- we don't recreate a network, if it exists
- we only stop a network if it's active, and so we avoid an exception
  saying the network is not active

* test: mock libvirt

* add integration tests for virt_net

* test: enable virt_net test on RedHat 7 and 8

* ci: use the unsupported alias

* tests that require privileged mode are run in VM

* virt_net/create raise unexpected libvirt exception

* import mock from units.compat

* virt_net: do not call create() on "active" network

* virt_net func test: only clean up the libvirt packages

* test: virt_net: don't use assert_called()

* virt_net: add the destructive alias

* move the test in virt_net dir

* test/virt_net: clean up the network at the end

test/units/modules/cloud/misc/virt_net/conftest.py

@@ -0,0 +1,69 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright: (c) 2019, Ansible Project
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+import pytest
+
+from ansible.modules.cloud.misc import virt_net
+
+from units.compat import mock
+
+
+virt_net.libvirt = None
+virt_net.HAS_VIRT = True
+
+
+class DummyNetwork():
+    def __init__(self, name, isActive=True):
+        self._name = name
+        self._isActive = isActive
+
+    def name(self):
+        return self._name
+
+    def isActive(self):
+        return self._isActive
+
+
+class DummyLibvirtConn():
+    def __init__(self):
+        self._network = [
+            DummyNetwork("inactive_net", isActive=False),
+            DummyNetwork("active_net", isActive=True)]
+
+    def listNetworks(self):
+        return [i.name() for i in self._network]
+
+    def networkLookupByName(self, name):
+        for i in self._network:
+            if i.name() == name:
+                return i
+
+    def listDefinedNetworks(self):
+        return []
+
+
+class DummyLibvirt():
+    VIR_ERR_NETWORK_EXIST = 'VIR_ERR_NETWORK_EXIST'
+
+    @classmethod
+    def open(cls, uri):
+        return DummyLibvirtConn()
+
+    class libvirtError(Exception):
+        def __init__(self):
+            self.error_code
+
+        def get_error_code(self):
+            return self.error_code
+
+
+@pytest.fixture
+def dummy_libvirt(monkeypatch):
+    monkeypatch.setattr(virt_net, 'libvirt', DummyLibvirt)
+    return DummyLibvirt
+
+
+@pytest.fixture
+def virt_net_obj(dummy_libvirt):
+    return virt_net.VirtNetwork('qemu:///nowhere', mock.MagicMock())