Add vfail and vsuccess interfaces

Add vfail and vsuccess interfaces

This now factorizes code needed to asprintf
the arguments in an allocated string.

But the most interesting effect is the ability
to handle va_list of arguments. It can be used
for library of tools.

Change-Id: I4ba74c9984786f07abe0c7e53d7ef79dca863735
Signed-off-by: José Bollo <jose.bollo@iot.bzh>