Made the beta clusters use deployment-mx for outgoing mail delivery

deployment-mx is the polonium equivallent in beta. This patch would make
every instance in the beta cluster to have route_list set to deployment-mx.
wmflabs.org. Shifting to a beta mx is necessary for testing future patch sets
that affect  mail system and polonium.
This was a FIXME in manifest/realm.pp

Change-Id: I7d7a6500391d8e30890ec04f1fd0a92b394a726f
Merge "Made the beta clusters use deployment-mx for outgoing mail delivery" into production