Send swift upload instructions to workers

Have zuul send signed credentials as part of the job for workers to
consume and upload assets to a defined location.

Zuul currently doesn't care about logs however this change will
suggest a LOG_PATH to builders as a unqiue destination prefix
allowing zuul to know preemptively the destination.
The workers are still required to send a URL of the final location.

Change-Id: I042cdd2dd2407f381cafcabc5c6b83d9b9a9eb00
diff --git a/doc/source/launchers.rst b/doc/source/launchers.rst
index f3e45db..accd80b 100644
--- a/doc/source/launchers.rst
+++ b/doc/source/launchers.rst
@@ -11,6 +11,8 @@
 .. _`Turbo-Hipster Documentation`:
    http://turbo-hipster.rtfd.org/
 
+.. _FormPost: http://docs.openstack.org/developer/swift/misc.html#module-swift.common.middleware.formpost
+
 .. _launchers:
 
 Launchers
@@ -117,6 +119,34 @@
 Your jobs can check whether the parameters are ``000000`` to act
 differently on each kind of event.
 
+Swift parameters
+~~~~~~~~~~~~~~~~
+
+If swift information has been configured for the job zuul will also
+provide signed credentials for the builder to upload results and
+assets into containers using the `FormPost`_ middleware.
+
+Each zuul container/instruction set will contain each of the following
+parameters where $NAME is the ``name`` defined in the layout.
+
+*SWIFT_$NAME_URL*
+  The swift destination URL. This will be the entire URL including
+  the AUTH, container and path prefix (folder).
+*SWIFT_$NAME_HMAC_BODY*
+  The information signed in the HMAC body. The body is as follows::
+
+    PATH TO OBJECT PREFIX (excluding domain)
+    BLANK LINE (zuul implements no form redirect)
+    MAX FILE SIZE
+    MAX FILE COUNT
+    SIGNATURE EXPIRY
+
+*SWIFT_$NAME_SIGNATURE*
+  The HMAC body signed with the configured key.
+*SWIFT_$NAME_LOGSERVER_PREFIX*
+  The URL to prepend to the object path when returning the results
+  from a build.
+
 Gearman
 -------