DNS suffix customization

[mook-as]

There was some short discussion on #integration, but I'm certainly up for more if that's desired. This is basically somewhere that lets me keep track of what's going on :)

This allows changing the DNS suffix used to look for other etcd nodes (instead of consul's etcd.service.cf.internal), for cases where a different service discovery mechanism is being used. If this lands as-is, the next step is to update manifest generation in cf-release and diego-release (anything else?) to add the property, then remove the default from the spec.

(I can't quite tell from the git history if I should be working from develop or master; the README wasn't very enlightening on that aspect. I'd be happy to rebase or whatever else to make the code sensible, first.)

If opening a story in a tracker to coordinate dealing with cf-release / diego-release is preferable, that's fine too, though it would be a bit harder for me to help out :)

[cfdreddbot]

Hey Mook-as!

Thanks for submitting this pull request! I'm here to inform the recipients of the pull request that you've already signed the CLA.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this. You can view the current status of your issue at: https://www.pivotaltracker.com/story/show/115002695.

[mook-as]

Updated PR per comments on Slack:

• Changed the property name to etcd.advertise_urls_dns_suffix
• Remove the comment about deprecation
• Drop handling empty strings (i.e. no suffix given).

[Amit-PivotalLabs]

Thanks, prioritized.