papr: add documentation to YAML and simplify context

Don't duplicate the actual image tag used in the context. Just print it
in the logs instead. That way there's no risk of it being outdated when
we bump the tag in the YAML.

.papr.sh

@@ -1,6 +1,8 @@
 #!/bin/bash
 set -xeuo pipefail
 
+echo "Targeting OpenShift Origin $OPENSHIFT_IMAGE_TAG"
+
 pip install -r requirements.txt
 
 # ping the nodes to check they're responding and register their ostree versions

.papr.yml

@@ -1,5 +1,16 @@
 ---
 
+# This YAML file is used by PAPR. It details the test
+# environment to provision and the test procedure. For more
+# information on PAPR, see:
+#
+#   https://github.com/projectatomic/papr
+#
+# The PAPR YAML specification detailing allowed fields can
+# be found at:
+#
+#   https://github.com/projectatomic/papr/blob/master/sample.papr.yml
+
 cluster:
   hosts:
     - name: ocp-master
@@ -19,7 +30,7 @@ packages:
   - openssl-devel
   - redhat-rpm-config
 
-context: 'fedora/25/atomic | origin/v3.6.0-alpha.1'
+context: 'fedora/25/atomic'
 
 env:
   OPENSHIFT_IMAGE_TAG: v3.6.0-alpha.1