GCE provider: Limit Filter calls to regexps rather than insane blobs

Filters can't exceed 4k, and GET requests against the GCE API are also
limited, so these break down in different ways at different cluster
counts. Fix it by introducing an advisory node-instance-prefix
configuration in the GCE provider that can hint the
EnsureLoadBalancer/UpdateLoadBalancer code (and the firewall
creation/update code). If it's not there, or wrong (a hostname that's
registered violates it), just ignore it and grab the whole project.

cluster/gce/configure-vm.sh

@@ -793,6 +793,7 @@ EOF
   if [[ -n "${NODE_INSTANCE_PREFIX:-}" ]]; then
     cat <<EOF >>/etc/gce.conf
 node-tags = ${NODE_INSTANCE_PREFIX}
+node-instance-prefix = ${NODE_INSTANCE_PREFIX}
 EOF
     CLOUD_CONFIG=/etc/gce.conf
   fi

cluster/gce/gci/configure-helper.sh

@@ -191,6 +191,7 @@ EOF
     use_cloud_config="true"
     cat <<EOF >>/etc/gce.conf
 node-tags = ${NODE_INSTANCE_PREFIX}
+node-instance-prefix = ${NODE_INSTANCE_PREFIX}
 EOF
   fi
   if [[ -n "${MULTIZONE:-}" ]]; then

cluster/gce/trusty/configure-helper.sh

@@ -334,6 +334,7 @@ EOF
     use_cloud_config="true"
     cat <<EOF >>/etc/gce.conf
 node-tags = ${NODE_INSTANCE_PREFIX}
+node-instance-prefix = ${NODE_INSTANCE_PREFIX}
 EOF
   fi
   if [ -n "${MULTIZONE:-}" ]; then