papr: Bump primary to f27

Let's start with just f27-primary for now.

Closes: #1350
Approved by: cgwalters

.papr.yml

@@ -4,10 +4,10 @@ branches:
     - try
 
 required: true
-context: f26-primary
+context: f27-primary
 
 container:
-    image: registry.fedoraproject.org/fedora:26
+    image: registry.fedoraproject.org/fedora:27
 
 env:
     # Enable all the sanitizers for this primary build.