Add version specific tags for V7 and V8 elasticsearch tests

to allow skipping V7 or V8 tests individually.

Change-Id: I20c005dbf183b3c07e0d032a06a147ec0c408510
diff --git a/BUILD b/BUILD
index 858c03a..205841b 100644
--- a/BUILD
+++ b/BUILD
@@ -85,6 +85,7 @@
     tags = [
         "docker",
         "elastic",
+        "elastic_V7",
         "exclusive",
     ],
     deps = ELASTICSEARCH_DEPS + PLUGIN_TEST_DEPS + [
@@ -104,6 +105,7 @@
     tags = [
         "docker",
         "elastic",
+        "elastic_V8",
         "exclusive",
     ],
     deps = ELASTICSEARCH_DEPS + PLUGIN_TEST_DEPS + [