Do etcd semver validation using posix only

hack/lib/etcd.sh

@@ -36,12 +36,12 @@ kube::etcd::validate() {
 
   # validate installed version is at least equal to minimum
   version=$(etcd --version | tail -n +1 | head -n 1 | cut -d " " -f 3)
-  if [[ "`echo -e "${version}\n${ETCD_VERSION}" | sort -rV | head -n 1`" != "$version" ]]; then
+  if [[ $(kube::etcd::version $ETCD_VERSION) -gt $(kube::etcd::version $version) ]]; then
    export PATH=$KUBE_ROOT/third_party/etcd:$PATH
    hash etcd
    echo $PATH
    version=$(etcd --version | head -n 1 | cut -d " " -f 3)
-   if [[ "`echo -e "${version}\n${ETCD_VERSION}" | sort -rV | head -n 1`" != "$version" ]]; then
+   if [[ $(kube::etcd::version $ETCD_VERSION) -gt $(kube::etcd::version $version) ]]; then
     kube::log::usage "etcd version ${ETCD_VERSION} or greater required."
     kube::log::info "You can use 'hack/install-etcd.sh' to install a copy in third_party/."
     exit 1
@@ -49,6 +49,10 @@ kube::etcd::validate() {
   fi
 }
 
+kube::etcd::version() {
+  printf '%s\n' "${@}" | awk -F . '{ printf("%d%03d%03d\n", $1, $2, $3) }'
+}
+
 kube::etcd::start() {
   # validate before running
   kube::etcd::validate