use vbox ubuntu/xenial64 and add memory to master/replica SUTs

change and pin vbox :

git diff spec/acceptance/nodesets/default.yml 
diff --git a/spec/acceptance/nodesets/default.yml b/spec/acceptance/nodesets/default.yml
index 23bb2cd..66f8234 100644
--- a/spec/acceptance/nodesets/default.yml
+++ b/spec/acceptance/nodesets/default.yml
@@ -41,7 +41,9 @@ HOSTS:
     - client-ubuntu16
     platform: ubuntu-1604-amd64
     hypervisor: vagrant
-    box: geerlingguy/ubuntu1604
+    box: ubuntu/xenial64
+    box_version: 20181114.0.0
+    box_check_update: false
     vagrant_memsize: 1024
     ip: 192.168.44.38