Rackspace: add region selection

git-svn-id: https://plugins.svn.wordpress.org/updraftplus/trunk@817427 b8457f37-d9ea-0310-8a92-e5e31aec5664
Rackspace: make new SDK default for PHP 5.3.3+

git-svn-id: https://plugins.svn.wordpress.org/updraftplus/trunk@817428 b8457f37-d9ea-0310-8a92-e5e31aec5664