use insights etag as a cache

* During insights project updates, if the etag from insights matches the
last etag (scm_revision) then don't get all the maintenance playbooks.
Otherwise, get all the maintenance playbooks and update scm_revision
with the etag.

awx/main/tasks.py

@@ -1291,7 +1291,8 @@ class RunProjectUpdate(BaseTask):
             'scm_clean': project_update.scm_clean,
             'scm_delete_on_update': project_update.scm_delete_on_update if project_update.job_type == 'check' else False,
             'scm_full_checkout': True if project_update.job_type == 'run' else False,
-            'scm_revision_output': self.revision_path
+            'scm_revision_output': self.revision_path,
+            'scm_revision': project_update.project.scm_revision,
         })
         args.extend(['-e', json.dumps(extra_vars)])
         args.append('project_update.yml')

awx/playbooks/project_update.yml

@@ -10,6 +10,7 @@
 # scm_username: username (only for svn)
 # scm_password: password (only for svn)
 # scm_accept_hostkey: true/false (only for git)
+# scm_revision: current revision in tower
 
 - hosts: all
   connection: local
@@ -105,20 +106,26 @@
         scm_version: "{{ scm_result['after'] }}"
       when: "'after' in scm_result"
 
+    - block:
       - name: update project using insights
         uri:
           url: "{{insights_url}}/r/insights/v1/maintenance?ansible=true"
           user: "{{scm_username}}"
           password: "{{scm_password}}"
           force_basic_auth: yes
-      when: scm_type == 'insights'
         register: insights_output
 
+      - name: Set the insights cache version
+        set_fact:
+          scm_version: "{{ insights_output.etag|default(scm_revision)|regex_replace('\"(.*)\"$', '\\1') }}"
+
+      when: scm_type == 'insights'
+
+    - block:
       - name: Ensure the project directory is present
         file:
           dest: "{{project_path|quote}}"
           state: directory
-      when: scm_type == 'insights'
 
       - name: Fetch Insights Playbook With Name
         get_url:
@@ -128,7 +135,7 @@
           url_password: "{{scm_password}}"
           force_basic_auth: yes
           force: yes
-      when: scm_type == 'insights' and item.name != None and item.name != ""
+        when: item.name != None and item.name != ""
         with_items: "{{ insights_output.json|default([]) }}"
         failed_when: false
 
@@ -140,10 +147,12 @@
           url_password: "{{scm_password}}"
           force_basic_auth: yes
           force: yes
-      when: scm_type == 'insights' and (item.name == None or item.name == "")
+        when: (item.name == None or item.name == "")
         with_items: "{{ insights_output.json|default([]) }}"
         failed_when: false
 
+      when: scm_type == 'insights' and scm_version != scm_revision
+
     - name: detect requirements.yml
       stat: path={{project_path|quote}}/roles/requirements.yml
       register: doesRequirementsExist