JT-branch docs and code cleanup

bump migration

fine tune validation of project allow_override
  return highly custom error message

Restore branch after syncs to address bugs
  encountered after changing scm_refspec

remove unused code to determine scm_revision

Check Ansible version before project update and
  do not install collections if Ansible version too old

Add docs related to project branch override
  New file specific to branch override and refspec
Complete docs on collections to reflect current
  implementation and give a folder tree example
Update clustering docs related to project syncs

Fix bug where git depth was ignored during the
  local clone from project folder to run folder

Fix bug where submodules were not copied

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

@@ -5,6 +5,7 @@ from django.conf import settings
 import pytest
 
 from awx.api.versioning import reverse
+from awx.main.models import Project, JobTemplate
 
 
 @pytest.mark.django_db
@@ -47,7 +48,7 @@ def test_project_unset_custom_virtualenv(get, patch, project, admin, value):
 
 
 @pytest.mark.django_db
-def test_no_changing_overwrite_behavior(post, patch, organization, admin_user):
+def test_no_changing_overwrite_behavior_if_used(post, patch, organization, admin_user):
     r1 = post(
         url=reverse('api:project_list'),
         data={
@@ -58,10 +59,38 @@ def test_no_changing_overwrite_behavior(post, patch, organization, admin_user):
         user=admin_user,
         expect=201
     )
+    JobTemplate.objects.create(
+        name='provides branch', project_id=r1.data['id'],
+        playbook='helloworld.yml',
+        scm_branch='foobar'
+    )
     r2 = patch(
         url=reverse('api:project_detail', kwargs={'pk': r1.data['id']}),
         data={'allow_override': False},
         user=admin_user,
         expect=400
     )
-    assert 'cannot be changed' in str(r2.data['allow_override'])
+    assert 'job templates already specify a branch for this project' in str(r2.data['allow_override'])
+    assert 'ids: 2' in str(r2.data['allow_override'])
+    assert Project.objects.get(pk=r1.data['id']).allow_override is True
+
+
+@pytest.mark.django_db
+def test_changing_overwrite_behavior_okay_if_not_used(post, patch, organization, admin_user):
+    r1 = post(
+        url=reverse('api:project_list'),
+        data={
+            'name': 'fooo',
+            'organization': organization.id,
+            'allow_override': True
+        },
+        user=admin_user,
+        expect=201
+    )
+    patch(
+        url=reverse('api:project_detail', kwargs={'pk': r1.data['id']}),
+        data={'allow_override': False},
+        user=admin_user,
+        expect=200
+    )
+    assert Project.objects.get(pk=r1.data['id']).allow_override is False