v1.10.0: [CP-18781] Use the correct vif device id in set_MTU or fail (#2760)

• Use the correct vif device id in set_MTU or fail
• Add force flag to VM.start
• Fix an issue where VM_metrics were assumed to exist
• Protect PIF.scan with a mutex to avoid duplicate PIFs
• Fix xe-toolstack-restart for mpathalert
• Rename mpathalert-daemon.service to mpathalert.service
• Pick up hvm value from xenopsd, report it on CLI
• Improve error messages in logs
• Fix unknown key iscsi_iqn backtrace
• Add 3 new fields to vm_metric: hvm, nested_virt, nomigrate