Add and validate namespace to pod, service, replication controller objects

Next iteration in delivering code against the integrated namespaces proposal, the PR adds the following:

1. Add Namespace to Pod, Service, ReplicationController objects
2. Enforces Namespace is set prior to persistence
3. Enforces context.Namespace on create and update operations matches resource.Namespace

Feedback welcome.

Track it further.

dnsSubdomainRegexp is dnsLabel(\.dnsLabel)*

dnsLabel is [a-z0-9]([-a-z0-9]*[a-z0-9])?

The net result is that it must be at least one character.

If you look at TestIsDNSSubdomain() you will see "" is tested as a badValue.  Likewise for TestIsDNSLabel()

Are you actually seeing that return true for "" or just extrapolating from code inspection?