Add EMS provider_region column; Undo hack for EmsAmazon to use hostname.

https://bugzilla.redhat.com/show_bug.cgi?id=1144523

In addition, this will enable us to support OpenStack regions in an analogous way to how we support Amazon regions.

@blomquisg @gmcculloug Please review
@dclarizio There is a small UI change here, so please review that one