Skip Elasticsearch backups against v2.x remote appliances

This is going to take some work to figure out. Skipping for now so
backup runs pass against v2.0 hosts.

Author: rtomayko

bin/ghe-backup

@@ -122,9 +122,13 @@ echo "Backing up GitHub Pages ..."
 ghe-backup-pages-${GHE_BACKUP_STRATEGY} ||
 failures="$failures pages"
 
-echo "Backing up Elasticsearch indices ..."
-ghe-backup-es-${GHE_BACKUP_STRATEGY} ||
-failures="$failures elasticsearch"
+if [ "$GHE_VERSION_MAJOR" -lt 2 ]; then
+    echo "Backing up Elasticsearch indices ..."
+    ghe-backup-es-${GHE_BACKUP_STRATEGY} ||
+    failures="$failures elasticsearch"
+else
+    echo "Skipping Elasticsearch backup under v2.x (not yet supported)"
+fi
 
 # If we're using the tarball backup strategy, bring the appliance out of
 # maintenance mode now instead of waiting until after pruning stale snapshots.