Separate the read preference per docstore.

This way you can change read preference for one of the module stores
without effecting the other.

Also fix whitespace.

playbooks/roles/edxapp/defaults/main.yml

@@ -566,7 +566,9 @@ edxapp_environment:
   # yaml based configs is complete
   CONFIG_ROOT: "{{ edxapp_app_dir }}"
 
-EDXAPP_LMS_MONGO_READ_PREFERENCE: 'PRIMARY'
+EDXAPP_LMS_DRAFT_MONGO_READ_PREFERENCE: 'PRIMARY'
+EDXAPP_LMS_SPLIT_MONGO_READ_PREFERENCE: 'PRIMARY'
+
 EDXAPP_CMS_MONGO_READ_PREFERENCE: 'PRIMARY'
 
 edxapp_generic_doc_store_config: &edxapp_generic_default_docstore
@@ -578,9 +580,13 @@ edxapp_generic_doc_store_config: &edxapp_generic_default_docstore
   collection:  'modulestore'
   ssl: "{{ EDXAPP_MONGO_USE_SSL }}"
 
-edxapp_lms_doc_store_config:
+edxapp_lms_draft_doc_store_config:
+  <<: *edxapp_generic_default_docstore
+  read_preference: "{{ EDXAPP_LMS_DRAFT_MONGO_READ_PREFERENCE }}"
+
+edxapp_lms_split_doc_store_config:
   <<: *edxapp_generic_default_docstore
-    read_preference: "{{ EDXAPP_LMS_MONGO_READ_PREFERENCE }}"
+  read_preference: "{{ EDXAPP_LMS_SPLIT_MONGO_READ_PREFERENCE }}"
 
 edxapp_cms_doc_store_config:
   <<: *edxapp_generic_default_docstore
@@ -788,14 +794,14 @@ lms_auth_config:
           stores:
             - NAME: 'split'
               ENGINE: 'xmodule.modulestore.split_mongo.split_draft.DraftVersioningModuleStore'
-              DOC_STORE_CONFIG: "{{ edxapp_lms_doc_store_config }}"
+              DOC_STORE_CONFIG: "{{ edxapp_lms_split_doc_store_config }}"
               OPTIONS:
                 default_class: 'xmodule.hidden_module.HiddenDescriptor'
                 fs_root:  "{{ edxapp_course_data_dir }}"
                 render_template: 'edxmako.shortcuts.render_to_string'
             - NAME: 'draft'
               ENGINE: 'xmodule.modulestore.mongo.DraftMongoModuleStore'
-              DOC_STORE_CONFIG: "{{ edxapp_lms_doc_store_config }}"
+              DOC_STORE_CONFIG: "{{ edxapp_lms_draft_doc_store_config }}"
               OPTIONS:
                 default_class: 'xmodule.hidden_module.HiddenDescriptor'
                 fs_root:  "{{ edxapp_course_data_dir }}"