support percona mongodb version output

* percona: Percona Server for MongoDB shell version v3.4.18-2.16
* rh-scl: MongoDB shell version v3.4.9

Author: h0tw1r3

lib/facter/mongodb_version.rb

@@ -2,7 +2,7 @@
   setcode do
     if Facter::Core::Execution.which('mongo')
       mongodb_version = Facter::Core::Execution.execute('mongo --version 2>&1')
-      %r{^MongoDB shell version:?\s+([\w\.]+)}.match(mongodb_version)[1]
+      %r{MongoDB shell version:?\s+v?([\w\.]+)}.match(mongodb_version)[1]
     end
   end
 end