Changed default scan_via_host value to false.

This value was originally set to true to ensure vddk scanning did not send all disk data through the VC.  This is not a realistic concern as VC returns a handle the the host for communication.

Switching the default value also removes the need to add host credentials solely for the purpose of VM scanning on VMware.
I would prefer leaving it exposed. It makes it easier to change in the field if there's a problem. I would also prefer having the default defined in the config file, it makes instructing someone on making the change easier - find the tag and change the value - instead of: find where the tag should be defined, then add the tag and value.