edxapp-git-auth: Add `EDXAPP_USE_GIT_IDENTITY` boolean to switch on/off

Using `EDXAPP_LOCAL_GIT_IDENTITY` gives parsing errors during evaluation for paths

playbooks/roles/edxapp/defaults/main.yml

@@ -131,6 +131,7 @@ EDXAPP_SANDBOX_ENFORCE: true
 EDXAPP_INCLUDE_AUTOMATOR_ROLE: false
 EDXAPP_AUTOMATOR_AUTHORIZED_KEYS: []
 
+EDXAPP_USE_GIT_IDENTITY: false
 # Example: "{{ secure_dir }}/files/git-identity"
 EDXAPP_LOCAL_GIT_IDENTITY: !!null
 

playbooks/roles/edxapp/tasks/deploy.yml

@@ -12,19 +12,19 @@
   template: >
     src=git_ssh_noauth.sh.j2 dest={{ edxapp_git_ssh }}
     owner={{ edxapp_user }} mode=750
-  when: not EDXAPP_LOCAL_GIT_IDENTITY
+  when: not EDXAPP_USE_GIT_IDENTITY
 
 - name: create ssh script for git (authenticated)
   template: >
     src=git_ssh_auth.sh.j2 dest={{ edxapp_git_ssh }}
     owner={{ edxapp_user }} mode=750
-  when: EDXAPP_LOCAL_GIT_IDENTITY
+  when: EDXAPP_USE_GIT_IDENTITY
 
 - name: install read-only ssh key
   copy: >
     src={{ EDXAPP_LOCAL_GIT_IDENTITY }} dest={{ edxapp_git_identity }}
     force=yes owner={{ edxapp_user }} mode=0600
-  when: EDXAPP_LOCAL_GIT_IDENTITY
+  when: EDXAPP_USE_GIT_IDENTITY
 
 # Do A Checkout
 - name: checkout edx-platform repo into {{edxapp_code_dir}}
@@ -56,7 +56,7 @@
 
 - name: remove read-only ssh key
   file: path={{ edxapp_git_identity }} state=absent
-  when: EDXAPP_LOCAL_GIT_IDENTITY
+  when: EDXAPP_USE_GIT_IDENTITY
 
 - name: create checksum for requirements, package.json and Gemfile
   shell: >