[libvirt] [PATCH] Unify *ReportError logic

Currently, most src/* files have their own ReportError function. Some support printf style arguments, others only allow reporting a single string message. The code for all of them does virtually the same thing, possibly passing a different constant off to another function. The attached patch adds a function to virterror.c which encapsulates the common ReportError logic. I used this to replace qemudReportError with a macro, which also allows passing off filename and line number info if we wanted to do something with it later. I did just the one function conversion to see what people think: if I'm missing something, or ideas for anything else to add. Seems to work as expected in my testing. Thanks, Cole