When deploy OpenStack on XenServer, we need install some XAPI
plugins to dom0. This commit is to add utils for this purpose.
If the os-xenapi version is different from the os-xenapi which
contains the utils. Users can specify the version to the utils.
So that the utils will download the right version of os-xenapi
and copy plugins from there. Otherwise the utils will by default
copy plugins from current installed packages.
Change-Id: I269a444b952f63fd73b3825b23dc95d6e825ce8f