Fix issue with GCE scripts assuming Python2.

For bug kubernetes#87482.
Newer OSs are now defaulting to Python3.
This breaks the kube-up scripts for GCE.
Adding code to detect this and explicitly use Python2.

Author: cheftako

cluster/gce/gci/configure-helper.sh

@@ -1527,7 +1527,7 @@ function start-kube-proxy {
 # $5: pod name, which should be either etcd or etcd-events
 function prepare-etcd-manifest {
   local host_name=${ETCD_HOSTNAME:-$(hostname -s)}
-  local host_ip=$(python -c "import socket;print(socket.gethostbyname(\"${host_name}\"))")
+  local host_ip=$(${PYTHON} -c "import socket;print(socket.gethostbyname(\"${host_name}\"))")
   local etcd_cluster=""
   local cluster_state="new"
   local etcd_protocol="http"
@@ -2713,17 +2713,21 @@ function main() {
 
   KUBE_HOME="/home/kubernetes"
   KUBE_BIN=${KUBE_HOME}/bin
+  PYTHON="python"
   CONTAINERIZED_MOUNTER_HOME="${KUBE_HOME}/containerized_mounter"
   PV_RECYCLER_OVERRIDE_TEMPLATE="${KUBE_HOME}/kube-manifests/kubernetes/pv-recycler-template.yaml"
 
+  if [[ "$(python -V)" =~ "Python 3" ]]; then
+    PYTHON="/usr/bin/python2.7"
+  fi
+
   if [[ ! -e "${KUBE_HOME}/kube-env" ]]; then
     echo "The ${KUBE_HOME}/kube-env file does not exist!! Terminate cluster initialization."
     exit 1
   fi
 
   source "${KUBE_HOME}/kube-env"
 
-
   if [[ -f "${KUBE_HOME}/kubelet-config.yaml" ]]; then
     echo "Found Kubelet config file at ${KUBE_HOME}/kubelet-config.yaml"
     KUBELET_CONFIG_FILE_ARG="--config ${KUBE_HOME}/kubelet-config.yaml"

cluster/gce/gci/configure.sh

@@ -64,7 +64,7 @@ function download-kube-env {
       -o "${tmp_kube_env}" \
       http://metadata.google.internal/computeMetadata/v1/instance/attributes/kube-env
     # Convert the yaml format file into a shell-style file.
-    eval $(python -c '''
+    eval $(${PYTHON} -c '''
 import pipes,sys,yaml
 for k,v in yaml.load(sys.stdin).iteritems():
   print("readonly {var}={value}".format(var = k, value = pipes.quote(str(v))))
@@ -103,7 +103,7 @@ function download-kube-master-certs {
       -o "${tmp_kube_master_certs}" \
       http://metadata.google.internal/computeMetadata/v1/instance/attributes/kube-master-certs
     # Convert the yaml format file into a shell-style file.
-    eval $(python -c '''
+    eval $(${PYTHON} -c '''
 import pipes,sys,yaml
 for k,v in yaml.load(sys.stdin).iteritems():
   print("readonly {var}={value}".format(var = k, value = pipes.quote(str(v))))
@@ -126,7 +126,7 @@ function validate-hash {
 # Get default service account credentials of the VM.
 GCE_METADATA_INTERNAL="http://metadata.google.internal/computeMetadata/v1/instance"
 function get-credentials {
-  curl --fail --retry 5 --retry-delay 3 ${CURL_RETRY_CONNREFUSED} --silent --show-error "${GCE_METADATA_INTERNAL}/service-accounts/default/token" -H "Metadata-Flavor: Google" -s | python -c \
+  curl --fail --retry 5 --retry-delay 3 ${CURL_RETRY_CONNREFUSED} --silent --show-error "${GCE_METADATA_INTERNAL}/service-accounts/default/token" -H "Metadata-Flavor: Google" -s | ${PYTHON} -c \
     'import sys; import json; print(json.loads(sys.stdin.read())["access_token"])'
 }
 
@@ -471,6 +471,11 @@ set-broken-motd
 
 KUBE_HOME="/home/kubernetes"
 KUBE_BIN="${KUBE_HOME}/bin"
+PYTHON="python"
+
+if [[ "$(python -V)" =~ "Python 3" ]]; then
+  PYTHON="/usr/bin/python2.7"
+fi
 
 # download and source kube-env
 download-kube-env