Make the Xen attach disk prefix configurable
Feature #1726: Metadata can be forced into .vmx files
(cherry picked from commit 83330906574692813dae20d96946d51260dcdd90)

Conflicts:
	src/vmm/LibVirtDriverVMware.cc
Feature #1726: Minor modifications to the driver
(cherry picked from commit 8ab717132d508765df272cfd6e615f437daefd87)
feature #1726: Removerepetated keys beforehand from the .vmx files
(cherry picked from commit 974552f46b3d0bfc1a292dd591a9df0abb488e8c)