tools: warning, ‘%.16x’ directive output truncated writing 16 bytes into a region...

tools: warning, ‘%.16x’ directive output truncated writing 16 bytes into a region of size 9.

The following warning appears during make.

    radosacl.cc:122:5: warning: ‘%.16x’ directive output truncated writing 16 bytes into a region of size 9 [-Wformat-truncation=]
     int main(int argc, const char **argv)
         ^~~~
                     from ./src/tools/radosacl.cc:19:
    /usr/include/bits/stdio2.h:65:44: note: ‘__builtin___snprintf_chk’ output 17 bytes into a destination of size 9
            __bos (__s), __fmt, __va_arg_pack ());

Signed-off-by: Jos Collin <jcollin@redhat.com>