Allow chef omnibus install.sh url to be configurable

[jrwesolo]

Inside ssh_base.rb, the url for the chef omnibus install.sh is currently hardcoded to https://www.opscode.com/chef/install.sh. This should be configurable to support custom variations that might be needed (such as in a corporate network, etc). This will also allow the possibility of removing an external dependency on opscode.com.

This pull request allows the url to be configured in the .kitchen.yml (example below)

driver config:
  require_chef_omnibus: true
  chef_omnibus_url: "https://example.com/chef/install.sh"

[fnichol]

Yes, great idea. I'd usually scrub this kind of hard coding sooner or later, so thank you.

Do you have an Opscode CLA signed by chance?

[jrwesolo]

My apologies. I set up an email filter and did not see your reply. I just signed up for an Opscode CLA under my same name and email and created the following ticket in jira: http://tickets.opscode.com/browse/KITCHEN-79. Is there anything else needed to be created?

[fnichol]

All right, thank you @jrwesolo!