Add web-ext-lint job report to the log folder

- Add fetch-web-ext-lint role, which copies the web-ext-lint report to
  the log folder.

Changes in the web-ext-lint job:
- Change the main playbook so the lint report is saved in a file called
  web-ext-lint.txt (so it can fetched later on).
- Add a post playbook which calls the fetch-web-ext-lint role.
- Add a description to the job.

Change-Id: Ifc2ef60084ecc33087e5ce2761ad91d84e7eff3c
diff --git a/playbooks/web-ext-lint/post.yaml b/playbooks/web-ext-lint/post.yaml
new file mode 100644
index 0000000..159ecf8
--- /dev/null
+++ b/playbooks/web-ext-lint/post.yaml
@@ -0,0 +1,4 @@
+- name: Get web-ext lint report
+  hosts: all
+  roles:
+    - fetch-web-ext-lint