make selfLink namespace aware
Merge pull request #2568 from derekwaynecarr/self_link_ns

make selfLink namespace aware
Add functions to get kubelet directories.

Gets rid of some magic constants and makes volume plugins (coming later)
cleaner.
Util to test if all ptr fields are nil
Add util to validate namespaced names
Move pkg/volume under kubelet
Add volume plugins scaffolding
empty_dir volume plugin
Move kubelet-specific code to kubelet.
host_mount volume plugin
git_repo volume plugin
gce_pd volume plugin
remove non-plugin mode for volumes
Add a util/mount pkg
use mount.Interface for GCE
move plugins to their own pkgs