Fix typo with ostype for puppet beaker jobs

Change-Id: I3c60c41c813d4c5fd5be93a1f7881df420f40658
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

jenkins/jobs/puppet-module-jobs.yaml

@@ -345,8 +345,7 @@
 
 - job-group:
     name: 'puppet-beaker-jobs-trusty'
-    ostype:
-      - trusty
+    ostype: trusty
     node:
       - ubuntu-trusty
     jobs:
@@ -354,8 +353,7 @@
 
 - job-group:
     name: 'puppet-beaker-jobs-centos7'
-    ostype:
-      - centos7
+    ostype: centos7
     node:
       - devstack-centos7
     jobs: