Rename uuid to build

We're providing more than one uuid to the job, so to make it clear
that one is for the build, and one is for the buildset, use those
words.

Change-Id: If9ebdc783dcef4f8dea9fa491b40ae49416e5cf1
diff --git a/doc/source/user/jobs.rst b/doc/source/user/jobs.rst
index beb489e..0b22252 100644
--- a/doc/source/user/jobs.rst
+++ b/doc/source/user/jobs.rst
@@ -121,7 +121,7 @@
 
 All items provide the following information as Ansible variables:
 
-**zuul.uuid**
+**zuul.build**
   The UUID of the build.  A build is a single execution of a job.
   When an item is enqueued into a pipeline, this usually results in
   one build of each job configured for that item's project.  However,
@@ -131,8 +131,6 @@
   job is run, for whatever reason, it is acompanied with a new
   unique id.
 
-.. TODO: rename build
-
 **zuul.buildset**
   The build set UUID.  When Zuul runs jobs for an item, the collection
   of those jobs is known as a buildset.  If the configuration of items