Modify VixDiskLib Client/Server to Use new ffi-vix_disk_lib gem

 Modify VixDiskLib Client/Server to Use new ffi-vix_disk_lib gem

Change the VixDiskLib client/server DRb code to use the
ffi-vixdisklib gem instead of the existing code in vixdisklib_api,
vixdisklib_server, and the contents of the VixDiskLib_FFI directory.
Interfaces to the gem include the direct-to-the-library "api", as well
as the "api_wrapper" which handles FFI-related memory management tasks.

Remove previously used code which is replaced by the gem code.

Add and modify functional tests to use the gem.