Updating to onos:2.2.6-rc1 and using released version of olt and dhcpl2relay apps. Releases voltha-onos:4.1.7

Change-Id: I3ee215bdc123693fbe0fbe957a9b7e4270d05a34
diff --git a/Dockerfile.voltha-onos b/Dockerfile.voltha-onos
index ef9bdf2..8a37a79 100644
--- a/Dockerfile.voltha-onos
+++ b/Dockerfile.voltha-onos
@@ -34,7 +34,7 @@
 
 
 # Unpack and install specific apps from download stage
-FROM onosproject/onos:2.2-latest as install
+FROM onosproject/onos:2.2.6-rc1 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:2.2-latest
+FROM onosproject/onos:2.2.6-rc1
 
 # The ENV settings must be replicated below as they are not shared between stages
 ENV ONOS=/root/onos