This refactor removes the legacy KubeletConfig object and adds a new
KubeletDeps object, which contains injected runtime objects and
separates them from static config. It also reduces NewMainKubelet to two
arguments: a KubeletConfiguration and a KubeletDeps.

Some mesos and kubemark code was affected by this change, and has been
modified accordingly.

And a few final notes:

KubeletDeps:
KubeletDeps will be a temporary bin for things we might consider
"injected dependencies", until we have a better dependency injection
story for the Kubelet. We will have to discuss this eventually.

RunOnce:
We will likely not pull new KubeletConfiguration from the API server
when in runonce mode, so it doesn't make sense to make this something
that can be configured centrally. We will leave it as a flag-only option
for now. Additionally, it is increasingly looking like nobody actually uses the
Kubelet's runonce mode anymore, so it may be a candidate for deprecation
and removal.