Allow specifying GCE network in GKE provider, default to "e2e" for tests

cluster/gke/config-default.sh

@@ -16,6 +16,7 @@
 
 # The following are default-specific settings.
 CLUSTER_NAME="${CLUSTER_NAME:-${USER}-gke}"
+NETWORK=${KUBE_GKE_NETWORK:-default}
 
 # For ease of maintenance, extract any pieces that do not vary between default
 # and test in a common config.

cluster/gke/config-test.sh

@@ -16,6 +16,7 @@
 
 # The following are test-specific settings.
 CLUSTER_NAME="${CLUSTER_NAME:-${USER}-gke-e2e}"
+NETWORK=${KUBE_GKE_NETWORK:-e2e}
 
 # For ease of maintenance, extract any pieces that do not vary between default
 # and test in a common config.

cluster/gke/util.sh

@@ -93,7 +93,8 @@ function kube-up() {
     --zone="${ZONE}" \
     --project="${PROJECT}" \
     --cluster-api-version="${CLUSTER_API_VERSION:-}" \
-    --num-nodes="${NUM_MINIONS}"
+    --num-nodes="${NUM_MINIONS}" \
+    --network="${NETWORK}"
 
   # Compute DNS_SERVER_IP: This is looking for something like
   # "servicesIpv4Cidr: 10.27.240.0/20" and returning "10.27.240"