upgrade linux worker setup scripts

tools/gce/create_linux_worker.sh

@@ -43,7 +43,7 @@ gcloud compute instances create $INSTANCE_NAME \
     --project="$CLOUD_PROJECT" \
     --zone "$ZONE" \
     --machine-type n1-standard-8 \
-    --image ubuntu-14-04 \
+    --image ubuntu-15-10 \
     --boot-disk-size 1000
 
 echo 'Created GCE instance, waiting 60 seconds for it to come online.'

tools/gce/linux_worker_init.sh

@@ -37,7 +37,7 @@ set -ex
 sudo apt-get update
 
 # Install JRE
-sudo apt-get install -y openjdk-7-jre
+sudo apt-get install -y openjdk-8-jre
 sudo apt-get install -y unzip lsof
 
 # Install Docker