Puppetfile: Fix missing trove commit

Currently the puppet-trove repository is pointing to an empty (ie. '')
commit in the Puppetfile causing r10k to fail with :

failed while running: Cannot check out unresolvable ref '' at
/etc/puppet/modules/trove

Change-Id: Id37cccf2cb390e5b36acc1ada1b2b7e42eddfaec

Puppetfile

@@ -52,7 +52,7 @@ mod 'tempest',
   :ref => 'f5e87cad5de119bd483006f06efcd22a34d8bdc4'
 mod 'trove',
   :git => 'git://github.com/enovance/puppet-trove.git',
-  :ref => ''
+  :ref => '16e82e68ea62efec3ec7e11d7b9887e16b773372'
 
 # Dependency
 mod 'apache',