Using released ONOS 2.5.7

Change-Id: I5bcbd966fa2b3b554e921f0ba4702d6ab1559dae
diff --git a/Dockerfile.voltha-onos b/Dockerfile.voltha-onos
index 2c36ef1..a76ea7f 100644
--- a/Dockerfile.voltha-onos
+++ b/Dockerfile.voltha-onos
@@ -34,7 +34,7 @@
 
 
 # Unpack and install specific apps from download stage
-FROM onosproject/onos:2.5.7-rc3 as install
+FROM onosproject/onos:2.5.7 as install
 
 # The ENV settings must be replicated below as they are not shared between stages
 ENV ONOS=/root/onos
@@ -58,7 +58,7 @@
 
 
 # Create the final image coping over the installed applications from the install stage
-FROM onosproject/onos:2.5.7-rc3
+FROM onosproject/onos:2.5.7
 
 # The ENV settings must be replicated below as they are not shared between stages
 ENV ONOS=/root/onos