labs: split out process_begin_files
labs: split out process_begin_files

Move the processing of *.begin status files into a separate function.
Call that function only if the host's status directory is shared with
the client scripts (through VirtualBox guest-additions).

Change-Id: I7716528c02aa4f8b5fc0901ff91ba5d37b5a0d9f

harrisonfeng/training-guides,Nabs007/training-guides,openstack/training-guides,harrisonfeng/training-guides,Nabs007/training-guides,openstack/training-guides,harrisonfeng/training-guides,Nabs007/training-guides