Introduce OOM reporting to virAsprintf

Actually, I'm turning this function into a macro as filename,
function name and line number needs to be passed. The new
function virAsprintfInternal is introduced with the extended set
of arguments.

tests/virbuftest.c

@@ -10,6 +10,8 @@
 #include "viralloc.h"
 #include "virstring.h"
 
+#define VIR_FROM_THIS VIR_FROM_NONE
+
 #define TEST_ERROR(...)                             \
     do {                                            \
         if (virTestGetDebug())                      \