add RFC952 label validation
Add requirements based scheduling.
Integration test on master, not just apiserver.

Moved code from cmd/apiserver to pkg/master.

test/integration/client_test made to use a master object,
instead of an apiserver.Handle.

Subsequent PRs will move more handler-installation into
pkg/master, with the goal that every http.Handler of a
standalone apiserver process can also be tested
in a "testing"-style go test.

In particular, a subsequent PR will test
authorization.
Merge pull request #1946 from brendandburns/scheduler

Add requirements based scheduling.
Merge pull request #1830 from markturansky/label_validation

add RFC952 validation to labels
Merge pull request #1978 from erictune/master_int_test

Integration test on master, not just apiserver.