new Rackspace API/SDK: bugfix

git-svn-id: https://plugins.svn.wordpress.org/updraftplus/trunk@816493 b8457f37-d9ea-0310-8a92-e5e31aec5664
new Rackspace API/SDK: increase chunk size

git-svn-id: https://plugins.svn.wordpress.org/updraftplus/trunk@816494 b8457f37-d9ea-0310-8a92-e5e31aec5664