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/zuul.d/jobs.yaml b/zuul.d/jobs.yaml
index 3db16ba..26bc4e6 100644
--- a/zuul.d/jobs.yaml
+++ b/zuul.d/jobs.yaml
@@ -2,3 +2,5 @@
     name: web-ext-lint
     pre-run: playbooks/web-ext-lint/pre.yaml
     run: playbooks/web-ext-lint/run.yaml
+    post-run: playbooks/web-ext-lint/post.yaml
+    description: Check a Web Extension project for basic lint problems.