Create backup_xenserver_vms_snapshot

This is a routine to backup virtual machines in Xenserver 6.0, 6.0.2, 6.2.
Its backup entirely vm to nfs storage across the network with compress using multi-threads pgiz.
Its create s snapshot from running virtual machine, then create a template and export this templete to network nfs storage. Then delete template and continue with another vm one by one. Default compress method using with xenserver uz gzip and use only one CPU.