Using the global tag instead of the defaults for 2.7 release in order to deploy the correct images

Change-Id: Ibf191297025ded5258221add3f1cf9de14bd9d80
diff --git a/releases/voltha-2.7 b/releases/voltha-2.7
index f92b32a..5251c57 100644
--- a/releases/voltha-2.7
+++ b/releases/voltha-2.7
@@ -15,8 +15,8 @@
 export HELM_VERSION=v3.2.4
 export KIND_VERSION=v0.8.1
 
-# defaults.image_tag=null will use the image tags in the Helm charts rather than
+# global.image_tag=null will use the image tags in the Helm charts rather than
 # kind-voltha's default which is 'master'.
 # Also we need to specify the tag for voltha/voltha-onos image since this is
 # not in the ONOS chart.
-export EXTRA_HELM_FLAGS="--set defaults.image_tag=null,images.onos.tag=4.3.1 "
+export EXTRA_HELM_FLAGS="--set global.image_tag=null,images.onos.tag=4.3.1 "