Add an API to determine the maven coordinates for an external artifact

Change-Id: Ief747497e2d02353aeb8515597f722aaf23cdf2e
diff --git a/tools/build/bazel/variables.bzl b/tools/build/bazel/variables.bzl
index 74b526e..ee80f7a 100644
--- a/tools/build/bazel/variables.bzl
+++ b/tools/build/bazel/variables.bzl
@@ -1 +1,2 @@
 ONOS_VERSION = "1.14.0-SNAPSHOT"
+ONOS_GROUP_ID = "org.onosproject"