nimbus.host is deprecated, support nimbus.seeds

[erikdw]

As @eyalzek pointed out, nimbus.host is deprecated in storm-1.0+. nimbus.seeds is the new config parameter we should be respecting in the MesosNimbus code.

The Nimbus spits out the following warning when you have nimbus.host:

Using deprecated config nimbus.host for backward compatibility. Please update your storm.yaml so it only has config nimbus.seeds

Note that it will be slightly nuanced to update the MesosNimbus code, as the nimbus.host value drives a couple of different behaviors, and the nimbus.seeds is based on an array of hosts, instead of 1 host.