[helios-client] Add checkNotNull preconditions on client

So if/when you mess it up, it's easier to see what you did wrong.
[helios-testing] Improve error message

Fixed to include the possibility that you forgot to put @Rule before
your TemporaryJobs member.
[helios-services] Remove unused import
[Vagrant] Fix Vagrantfile build of skydns

They changed the location of one of their dependencies, and that
dependency was no longer available in the old location so it
would no longer build
[system-tests] Fix warnings in MasterRespondsWithNoZKTest

It had getChildren throwing a checked exception when it doesn't
throw checked exceptions.
Merge pull request #91 from spotify/drewc/miscfix

Drewc/miscfix