[WIP] Modify VixDiskLib client/server code to use the new ffi-vixdisklib gem.

Change the VixDiskLib client/server DRb code to use the ffi-vix_disk_lib gem instead 
of the existing code in vixdisklib_api, vixdisklib_server, and the contents of the 
VixDiskLib_FFI directory.

Two different interfaces to the new gem exist via the "api" layer - direct to the vmware library,
and the "api_wrapper" layer, which performs ffi memory management functionality.

This commit changes an existing file to a "miq_wrapper" within ManageIQ which applies
a top-level wrapper which interacts with the DRb server code.

The ffi-vix_disk_lib gem is available in a repo under manageiq/ffi-vixdisklib and is ready to be
built along with this code.

@Fryguy @roliveri @jrafanie @chessbyte  Please review for sanity in using the gem.
For now, until we release the gem, you can probably put the following:

```ruby
gem "ffi-vix_disk_lib", :git => "git://github.com/ManageIQ/ffi-vix_disk_lib.git"
```

This would allow any specs on manageiq to probably still work properly.  You would also be able to test your branch locally with the "real" gem code, verifying that it works as expected.