Minor improvements in the HostVirtual driver and add new ex_get_node and
ex_build_node extension method.

Contributed by Dinesh Bhoopathy, part of LIBCLOUD-249.


git-svn-id: https://svn.apache.org/repos/asf/libcloud/trunk@1442703 13f79535-47bb-0310-9956-ffa450edef68