configure mtu explicitly for drone

this works around an issue on c3.* instances; see Docker bug:

https://github.com/dotcloud/docker/issues/4378

and this mail thread:

https://groups.google.com/forum/#!topic/docker-user/9klZLLPFG1I
remove cf- prefix from templates

Signed-off-by: Max Brunsfeld <mbrunsfeld@pivotallabs.com>