Run hack/verify-govet.sh as part of verify make target

This commit ensures that:
- go vet will be run as part of the make verify target
- the vet make-rule script won't be run directly, as generated_files won't be run in that case
- that go vet errors show up in the build log with a start time, finish time, and SUCCESS/FAILED message as part of the verify make rule script

hack/make-rules/vet.sh

@@ -23,9 +23,16 @@ source "${KUBE_ROOT}/hack/lib/init.sh"
 
 cd "${KUBE_ROOT}"
 
+# If called directly, exit.
+if [[ "${CALLED_FROM_MAIN_MAKEFILE:-""}" == "" ]]; then
+    echo "ERROR: $0 should not be run directly." >&2
+    echo >&2
+    echo "Please run this command using \"make vet\""
+    exit 1
+fi
+
 # This is required before we run govet for the results to be correct.
 # See https://github.com/golang/go/issues/16086 for details.
-make generated_files
 go install ./cmd/...
 
 # Use eval to preserve embedded quoted strings.
@@ -46,5 +53,4 @@ if [[ ${#targets[@]} -eq 0 ]]; then
   targets=$(go list -e ./... | egrep -v "/(third_party|vendor|staging|clientset_generated)/")
 fi
 
-set -x
 go vet "${goflags[@]:+${goflags[@]}}" ${targets[@]}