added replacement of unhandled char in xen vm name

Make the disallow_spaces_in_name = true is Hypervisor type is XEN
Add a list of unhandled char and delete them if Hypervisor is XEN
Merge branch 'xen-improvements' of https://github.com/CyrilPeponnet/Archipel into pr-643

Conflicts:
	ArchipelAgent/archipel-agent/archipel/archipelHypervisor.py
remove trailing space