Pin stdlib Puppet module to the last known good commit

puppetlabs/puppetlabs-stdlib@4f19c27
seems to have broken the ensure_resource() stdlib function for us.
Pinning to the last known good commit until a permanent fix is found.

Change-Id: Ic072350bc5961e4e65bf74a33ed42ccbdba9e98f

Puppetfile

@@ -150,7 +150,7 @@ mod 'ssh',
 
 mod 'stdlib',
   :git => 'https://github.com/puppetlabs/puppetlabs-stdlib',
-  :ref => 'master'
+  :ref => 'f15cc31041cb902d0025f1e35d9403956ad2fc79'
 
 mod 'sysctl',
   :git => 'https://github.com/duritong/puppet-sysctl',