Part two: configure ubuntu DomU VM and introduce
install-devstack-xen.sh
Move tools/xen from devstack to os-xenapi which will be the center
place to hold some XenServer/XenAPI specify source code.
This part is used to configure a DomU VM and install devstack on
domu VM
Change-Id: I20f4663d987266d6ff6d57c5eb3c4447d51f9162