create the Galaxy credential for new installs in the preload script

doing this in the migration *before* any Organizations actually exist
is stirring up RBAC dragons that I don't have time to fight

this commit meanst that *new* installs will pre-create the default
Galaxy (public) credential in create_preload_data, while
*upgraded/migrations* installs will do so via the migration

awx/main/management/commands/create_preload_data.py

@@ -42,6 +42,16 @@ class Command(BaseCommand):
                                               },
                                               created_by=superuser)
                 c.admin_role.members.add(superuser)
+                public_galaxy_credential = Credential(
+                    name='Ansible Galaxy',
+                    managed_by_tower=True,
+                    credential_type=CredentialType.objects.get(kind='galaxy'),
+                    inputs = {
+                        'url': 'https://galaxy.ansible.com/'
+                    }
+                )
+                public_galaxy_credential.save()
+                o.galaxy_credentials.add(public_galaxy_credential)
                 i = Inventory.objects.create(name='Demo Inventory',
                                              organization=o,
                                              created_by=superuser)

awx/main/migrations/_galaxy.py

@@ -14,9 +14,12 @@ logger = logging.getLogger('awx.main.migrations')
 
 
 def migrate_galaxy_settings(apps, schema_editor):
+    Organization = apps.get_model('main', 'Organization')
+    if Organization.objects.count() == 0:
+        # nothing to migrate
+        return
     set_current_apps(apps)
     ModernCredentialType.setup_tower_managed_defaults()
-    Organization = apps.get_model('main', 'Organization')
     CredentialType = apps.get_model('main', 'CredentialType')
     Credential = apps.get_model('main', 'Credential')
     Setting = apps.get_model('conf', 'Setting')