Model changes for instance last_seen field to replace modified (#10870)

* Model changes for instance last_seen field to replace modified

* Break up refresh_capacity into smaller units

* Rename execution node methods, fix last_seen clustering

* Use update_fields to make it clear save only affects capacity

* Restructing to pass unit tests

* Fix bug where a PATCH did not update capacity value

awx/main/tests/functional/api/test_instance.py

@@ -0,0 +1,32 @@
+import pytest
+
+from awx.api.versioning import reverse
+
+from awx.main.models.ha import Instance
+
+
+@pytest.mark.django_db
+def test_disabled_zeros_capacity(patch, admin_user):
+    instance = Instance.objects.create(hostname='example-host', cpu=6, memory=36000000000, cpu_capacity=6, mem_capacity=42)
+
+    url = reverse('api:instance_detail', kwargs={'pk': instance.pk})
+
+    r = patch(url=url, data={'enabled': False}, user=admin_user)
+    assert r.data['capacity'] == 0
+
+    instance.refresh_from_db()
+    assert instance.capacity == 0
+
+
+@pytest.mark.django_db
+def test_enabled_sets_capacity(patch, admin_user):
+    instance = Instance.objects.create(hostname='example-host', enabled=False, cpu=6, memory=36000000000, cpu_capacity=6, mem_capacity=42, capacity=0)
+    assert instance.capacity == 0
+
+    url = reverse('api:instance_detail', kwargs={'pk': instance.pk})
+
+    r = patch(url=url, data={'enabled': True}, user=admin_user)
+    assert r.data['capacity'] > 0
+
+    instance.refresh_from_db()
+    assert instance.capacity > 0