Make module id of discovery server and dns agent consistent:
a) Change DnsAgent to contrail-dns
b) Change contrail-discovery:0 to contrail-discovery

Change-Id: Ib78ec93804e3e1e513235f74de0fb02c0d7796ae
Closes-PR: 1383577
Merge "Make module id of discovery server and dns agent consistent: a) Change DnsAgent to contrail-dns b) Change contrail-discovery:0 to contrail-discovery"