Use 2.0.0-ONAP tag instead beijing branch

To ensure reproducible deployments, change gerrit branches to
2.0.0-ONAP tag instead of using the beijing branch since the
beijing branches are not locked.

Change-Id: I30bbece5fa2e0b8622db948d45e08a46ecf43ece
Issue-ID: INT-506
Signed-off-by: Gary Wu <gary.i.wu@huawei.com>
diff --git a/.gitreview b/.gitreview
index eabfdc6..8f5c6a0 100644
--- a/.gitreview
+++ b/.gitreview
@@ -2,4 +2,4 @@
 host=gerrit.onap.org
 port=29418
 project=oom
-defaultbranch=master
+defaultbranch=beijing