Deterministic ordering of port ranges in GetMachinePorts.

Order was dependent on map key ordering. Broken in Go 1.3+
Merge pull request #1177 from cmars/cmars-004-firewaller-mapfix

Deterministic ordering of port ranges in GetMachinePorts.

Fix intermittent failures in apiserver/firewaller caused by map key order dependence.

(Review request: http://reviews.vapour.ws/r/488/)