Allow user to pass extra arguments via "extra_args" argument which are
then passed to the "deployVirtualMachine" call in the CloudStack driver
create_node method.

Part of LIBCLOUD-330.


git-svn-id: https://svn.apache.org/repos/asf/libcloud/trunk@1486282 13f79535-47bb-0310-9956-ffa450edef68