Add go_genrule for zz_generated.openapi.go.

Clean zz_generated.openapi.go before running gazel.

hack/verify-bazel.sh

@@ -22,6 +22,10 @@ source "${KUBE_ROOT}/hack/lib/init.sh"
 
 go get gopkg.in/mikedanese/gazel.v16/gazel
 
+# Remove generated files prior to running gazel.
+# TODO(spxtr): Remove this line once Bazel is the only way to build.
+rm -f "${KUBE_ROOT}/pkg/generated/openapi/zz_generated.openapi.go"
+
 for path in ${GOPATH//:/ }; do
   if [[ -e "${path}/bin/gazel" ]]; then
     gazel="${path}/bin/gazel"
@@ -33,6 +37,7 @@ if [[ -z "${gazel:-}" ]]; then
   exit 1
 fi
 
+
 if ! "${gazel}" -validate -print-diff -root="$(kube::realpath ${KUBE_ROOT})" ; then
   echo
   echo "Run ./hack/update-bazel.sh"