Clean up /edx/var/edxapp/staticfiles before paver runs

When running on a dirty image (such as a sandbox base image or an AMI
build) this clears static files so that collectstatic will copy
everything.

Django's collectstatic copies files and doesn't preserve timestamps,
then only copies "newer modified files".  This leads to a condition
where old static files are in /edx/var/edxapp/staticfiles with a
timestamp of Yesterday, and we add a new dep which comes down from npm
with a timestamp of last week.  Collectstatic will not copy those.

playbooks/roles/edxapp/tasks/service_variant_config.yml

@@ -126,6 +126,24 @@
   tags:
     - migrate
 
+# There are problems with django collectstatic copying files.  It doesn't retain
+# last modified timestamps, but relies on those same timestamps to know if a new file
+# should be recopied.  While collectstatic --clear exists, it only clears some of the
+# files in edxapp_staticfile_dir, it leaves postprocessed or otherwise hashed files.
+# This ensures we have a totally clean directory.
+- name: Remove and recreate the staticfiles directory so nothing stale can exist
+  file:
+      path: "{{ edxapp_staticfile_dir }}"
+      state: "{{ item }}"
+      owner: "{{ edxapp_user }}"
+      group: "{{ common_web_group }}"
+      mode:  0755
+  when: celery_worker is not defined and not devstack
+  with_items: ['absent', 'directory']
+  tags:
+    - gather_static_assets
+    - assets
+
 # Gather assets using paver if possible
 - name: "gather {{ item }} static assets with paver"
   command: "{{ COMMON_BIN_DIR }}/edxapp-update-assets-{{ item }}"