Add parsing for multiple "public network" values.

[mdsteveb]

This is a first pass at a fix for issue #131. ("It works for me!")

[hufman]

Does having multiple networks in "public network" help for deployments where different servers are in different network ranges? When I tried running a mon with a multiple "public network" option, it used the first network and ignored the second. If that's intentional, than I think this looks good, and it worked in my tests.

[mdsteveb]

That's my use case; I have a 3rd mon in another building on another subnet (but on the same LAN of course). My interpretation of the Ceph networking docs was that it was just looking for an interface which matched something in the public network list to choose as its public network. It didn't look like there was any intent to actually be able to select multiple interfaces or IPs simultaneously, but I wasn't looking for that either.

[mdsteveb]

I should add that I'm having another problem after this in the deployment process and I can't tell if it's related. It's no longer crashing chef-client, but all my mon nodes are stuck on ceph-create-keys which of course is preventing anything else from working.

[hufman]

Code style checks out good, I like it!