ci: install the correct node.js version via nvm (elastic/elasticsearch#3229)

This will ensure that CI runs the Kibana plugin tests with the
appropriate version of node.js.

Original commit: elastic/x-pack-elasticsearch@aeb7399f91

dev-tools/ci

@@ -4,9 +4,13 @@
 # It will attempt to check out 'elasticsearch' into a sibling directory
 # unless the environment variable `USE_EXISTING_ES` has a value
 #
+# It will also attempt to install the appropriate version of node.js
+# for the Kibana plugin tests using nvm. Set a custom nvm directory
+# using the `NVM_DIR` environment variable.
+#
 
 # Turn on semi-strict mode
-set -euf pipefail
+set -e pipefail
 
 SCRIPT="$0"
 
@@ -51,11 +55,30 @@ else
     fi
 fi
 
+# back to base directory
+cd "$BASE_DIR"
+
+# install the correct node.js version
+if [ -z ${NVM_DIR:+x} ]; then
+  export NVM_DIR="/var/lib/jenkins/.nvm";
+fi
+
+NVM_SCRIPT="$NVM_DIR/nvm.sh"
+if [ -s "$NVM_SCRIPT" ]; then
+  . "$NVM_SCRIPT"  # load nvm
+else
+  echo "Unable to find the nvm script at \"$NVM_SCRIPT\""
+  exit 1
+fi
+
+echo "Installing node.js version $(cat ./kibana/.node-version)..."
+nvm install "$(cat ./kibana/.node-version)"
+
 echo "Running X-Plugins tests..."
-cd "$BASE_DIR" && echo "Running in $PWD"
+echo "Running in $PWD"
 
 # output the commands
-set -x
+set -xuf
 
 # clean
 gradle --stacktrace clean