[CPS] update .gitreview for london

- update .gitreview for dmi-plugin to change defaultbranch from master
  to london
- Step 13 of the release process

Issue-ID: CPS-1611
Change-Id: I783b3b273caeb50ad1bd4b95b3e451bfb404d86f
Signed-off-by: mpriyank <priyank.maheshwari@est.tech>
diff --git a/.gitreview b/.gitreview
index 26b3266..42df9a0 100644
--- a/.gitreview
+++ b/.gitreview
@@ -3,4 +3,4 @@
         host=gerrit.onap.org
         port=29418
         project=cps/ncmp-dmi-plugin
-        defaultbranch=master
+        defaultbranch=london