Return VixDiskLib Load Error to DRB Client

When VixDiskLibServer fails to successfully load any
version of the VixDiskLib, cache the failure reason.  
Interrogate for the error once the DRB service is started 
so that the failure reason can be passed back to the client 
for presentation in the UI. Then shut down the DRB service.

@roliveri, @jrafanie, @chessbyte please review
This is a constant, but you're treating it as a variable. Even if you're only setting it once,
wouldn't it be better if this were an instance variable?