The xen tools have been moved to the project of *os-xenapi* since
os-xenapi 0.3.0. We also did some refact work on these tools in
os-xenapi. This commit is to remove these tools from devstack. So
that os-xenapi will be the single place for xen tools.
Change-Id: I4fdbe6bce12dfedd0d1e975ab8dd624ee3740c11