test(pillar): centralise and clean-up entries

test/salt/pillar/salt.sls

 # vim: ft=yaml
 ---
 salt:
+  py_ver: 'py3'
+  # Override used for FreeBSD minion service
+  retry_options:
+    attempts: 5
   master:
     fileserver_backend:
       - rootfs

test/salt/pillar/v3001-py3.sls

 ---
 salt:
   release: '3001'
-  py_ver: 'py3'

test/salt/pillar/v3002-py3.sls

 ---
 salt:
   release: '3002'
-  py_ver: 'py3'
-
-  # Override used for FreeBSD minion service
-  retry_options:
-    attempts: 5
-    until: true
-    interval: 10
-    splay: 10

test/salt/pillar/v3003-py3.sls

 ---
 salt:
   release: '3003'
-  py_ver: 'py3'
-
-  # Override used for FreeBSD minion service
-  retry_options:
-    attempts: 5
-    until: true
-    interval: 10
-    splay: 10