Remove kubectl's dependence on schema file in pkg/api/validation.

**What this PR does / why we need it**:

Makes functions in validation/schema.go private to kubectl,
further isolating kubectl.

**Which issue this PR fixes**

Part of a series of PRs to address kubernetes/community#598

**Release note**:
```release-note
NONE
```

hack/lib/BUILD

@@ -1,5 +1,21 @@
 package(default_visibility = ["//visibility:public"])
 
+sh_library(
+    name = "lib",
+    srcs = [
+        "etcd.sh",
+        "golang.sh",
+        "init.sh",
+        "swagger.sh",
+        "test.sh",
+        "util.sh",
+        "version.sh",
+    ],
+    deps = [
+        "//cluster/lib",
+    ],
+)
+
 filegroup(
     name = "package-srcs",
     srcs = glob(["**"]),