Build k8s using latest commit of golang

Run "gimme master" and use the newly built binaries. Adjust
GOROOT_BOOTSTRAP so we can use the golang that is already
on disk to build the new commit from golang.

To enable this, edit `.go-version` and set the version to
```
devel
```

and then run `make quick-release` (for example)

Signed-off-by: Davanum Srinivas <davanum@gmail.com>

hack/lib/golang.sh

@@ -524,6 +524,18 @@ kube::golang::internal::verify_go_version() {
   if [ "${GOTOOLCHAIN:-auto}" != 'auto' ]; then
     # no-op, just respect GOTOOLCHAIN
     :
+  elif [ "${GO_VERSION:-}" == 'devel' ]; then
+    # get the latest master version of Go, build and use that version
+    export GOTOOLCHAIN='local'
+    if [[ ! -f "${KUBE_ROOT}/.gimme/envs/gomaster.env" && ! -f "${HOME}/.gimme/envs/gomaster.env" ]]; then
+      GOROOT_BOOTSTRAP="${GOROOT_BOOTSTRAP:-/usr/local/go}" "${KUBE_ROOT}/third_party/gimme/gimme" "master" >/dev/null 2>&1
+    fi
+
+    if [[ -f "${KUBE_ROOT}/.gimme/envs/gomaster.env" ]]; then
+      source "${KUBE_ROOT}/.gimme/envs/gomaster.env"
+    elif [[ -f "${HOME}/.gimme/envs/gomaster.env" ]]; then
+      source "${HOME}/.gimme/envs/gomaster.env"
+    fi
   elif [ -n "${FORCE_HOST_GO:-}" ]; then
     # ensure existing host version is used, like before GOTOOLCHAIN existed
     export GOTOOLCHAIN='local'

third_party/gimme/gimme

@@ -314,8 +314,10 @@ _setup_bootstrap() {
 # _compile "dir"
 _compile() {
 	(
-		if grep -q GOROOT_BOOTSTRAP "${1}/src/make.bash" &>/dev/null; then
-			_setup_bootstrap || return 1
+	  if [[ -z "${GOROOT_BOOTSTRAP}" ]]; then
+		  if grep -q GOROOT_BOOTSTRAP "${1}/src/make.bash" &>/dev/null; then
+			  _setup_bootstrap || return 1
+		  fi
 		fi
 		cd "${1}"
 		if [[ -d .git ]]; then