Add support for API version 5.1 to the vCloud driver and accept any value
which is a multiple of four for ex_vm_memory kwarg in create_node method.

Contributed by Trevor Powell part of LIBCLOUD-314.


git-svn-id: https://svn.apache.org/repos/asf/libcloud/trunk@1467555 13f79535-47bb-0310-9956-ffa450edef68