Simplify DNS validation checks

Move DNS length checks to util/validation.go.  Make the max subdomain be 253,
which is what the RFC actually says.
Add validation of VolumeMounts
Add validation of Ports

Also do caseless compares for "enum" strings.
Validation of HostPorts and Manifest IDs

Check that HostPorts are unique across the whole host and that Manifest IDs
are unique.
Instantiate cAdvisor client for kubelet to query both machine and container
information.
Merge pull request #377 from dchen1107/cadvisor1

Instantiate cAdvisor client for kubelet
Merge pull request #375 from thockin/valid/dns_lengths

Simplify DNS validation checks
Merge pull request #358 from thockin/valid2

Add validation of VolumeMounts
Add a note wrt. needing storage & storage apis on.
Tighten the identifiers spec

As I read through it I wanted to wordsmith a bit, which lead to reordering
some to read sort of top-down. There were a couple things I thought were wrong
(pod name should be a subdomain) and a few things I think we can make more
concise. I also added examples and clarified implications.