Add flag for turning off successful job logs

As a relief valve for times of storage pressure on the receiving end,
add a flag that can be set to skip log uploads for sucessful jobs.

It uses the same logic as emit-ara-html.

zuul_site_upload_logs == true (the default) will always upload logs
zuul_site_upload_logs == false will never upload logs
zuul_site_upload_logs == 'failure' will only upload failure logs

Setting this variable should be done in site variables.

Change-Id: I2a55730976520b75dcc98f86f34b7929f9243e62

roles/upload-logs/README.rst

@@ -12,3 +12,12 @@ This uploads logs to a static webserver using SSH.
    :default: /srv/static/logs
 
    The root path to the logs on the logserver.
+
+.. zuul:rolevar:: zuul_site_upload_logs
+   :default: true
+
+   Controls when logs are uploaded. true, the default, means always upload
+   logs. false means never upload logs. 'failure' means to only upload logs
+   when the job has failed.
+
+   .. note:: Intended to be set by admins via site-variables.

roles/upload-logs/tasks/main.yaml

@@ -2,9 +2,9 @@
   include_role:
     name: set-zuul-log-path-fact
 
-# NOTE(mordred) Temporary hack to only upload logs on failures to work around
-# unfortunately timed disk outage.
-- when: not zuul_success|bool
+# Always upload (true), never upload (false) or only on failure ('failure')
+- when: zuul_site_upload_logs | default(true) | bool or
+        (zuul_site_upload_logs == 'failure' and not zuul_success | bool)
   block:
 
     - name: Create log directories