Add NTP tarball

We're using a tarball import because the upstream project uses BitKeeper
for source control, and we don't think it's worth the effort of adding
BitKeeper support to Lorry for one project.
Merge branch 'jmac/add-ntp'

Reviewed-By: Francisco Redondo Marchena <francisco.marchena@codethink.co.uk>
Reviewed-By: Sam Thursfield <sam.thursfield@codethink.co.uk>
update leveldb host repo url
Add lorry for the github maintained snappy source
Correct the name for snappy-git lorry
Merge remote-tracking branch 'pdar/pd'

Reviewed-By: Pedro Alvarez <pedro.alvarez@codethink.co.uk>
Reviewed-By: Sam Thursfield <sam.thursfield@codethink.co.uk>