Switch to using puppetlabs/ntp

Puppetlabs ntp is under much more active development and is supported by
puppet. Win!

Also, this puppet module detects when it's running in a virtual machine
and disables tinker panic as VMware suggests
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006427
Merge pull request #606 from alphagov/upgrade-ntp

Switch to using puppetlabs/ntp