BoxCI should use the literal image name specified in the openstack config file instead of using Regex

[jlevis]

BoxCI should use the literal image name specified in the openstack config file instead of using Regex. Otherwise, we run into an issue where another image containing the same text in its name could be picked up unintentionally.

This:
os.image = Regexp.new('<%= @provider_config.fetch("image") -%>')

Should be this:
os.image = "<%= @provider_config.fetch("image") -%>"

In this file:
https://github.com/reachlocal/boxci/blob/master/lib/boxci/templates/providers/openstack/Vagrantfile.erb#L14