Add basic Authorization.

Added basic interface for authorizer implementations.
Added default "authorize everything" and "authorize nothing
implementations.
Added authorization check immediately after authentication check.
Added an integration test of authorization at the HTTP level of
abstraction.

hack/test-integration.sh

@@ -41,7 +41,7 @@ start_etcd
 echo ""
 echo "Integration test cases..."
 echo ""
-GOFLAGS="-tags 'integration no-docker'" \
+GOFLAGS="-tags 'integration no-docker' -test.v" \
   "${KUBE_ROOT}/hack/test-go.sh" test/integration
 
 echo ""