Upload logs to a swift container

This uploads logs to an OpenStack Object Store (Swift) container.

**Role Variables**

.. 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.

.. zuul:rolevar:: zuul_log_cloud_config

   Complex argument which contains the cloud configuration in
   os-cloud-config (clouds.yaml) format.  It is expected that this
   argument comes from a `Secret`.

.. zuul:rolevar:: zuul_log_partition
   :default: false

   If set to true, then the first component of the log path will be
   removed from the object name and added to the container name, so
   that logs for different changes are distributed across a large
   number of containers.

.. zuul:rolevar:: zuul_log_container
   :default: logs

   This role will create containers which do not already exist.  If
   partitioning is not enabled, this is the name of the container
   which will be used.  If partitioning is enabled, then this will be
   used as the prefix for the container name which will be separated
   from the partition name by an underscore.  For example, "logs_42"
   would be the container name for partition 42.

.. zuul:rolevar:: zuul_log_container_public
   :default: true

   If the container is created, should it be created with global read
   ACLs.  If the container already exists, it will not be modified.

.. zuul:rolevar:: zuul_log_delete_after
   :default: 15552000

   Number of seconds to delete objects after upload. Default is 6 months
   (15552000 seconds) and if set to 0 X-Delete-After will not be set.

.. zuul:rolevar:: zuul_log_path
   :default: Generated by the role `set-zuul-log-path-fact`

   Prepend this path to the object names when uploading.