ESX: Change disk selection for datastore detection.

ESX: Change disk selection for datastore detection.

In order to register a new virtual machine the ESX driver needs to upload
a VMX file to a datastore. Try to put this file beside the main VMDK file
of the virtual machine. Change the disk selection for datastore detection
to choose the first file-based harddisk instead of just the first disk.
The first disk may be a CDROM disk and ISO images are normaly not located
in the virtual machine's directory.

* src/esx/esx_driver.c: change disk selection for datastore detection