tests-util: Adding test to verify "no-conversion" detection

tests-util: Adding test to verify "no-conversion" detection

The standard string to integer conversion routines return zero
if a string was to be converted which did not reflect a number.
It is not flag'ed as an error.
The wrapper functions strtoul_err() and strtoull_err() are expected
to exactly do this.

Signed-off-by: Swen Schillig <swen@linux.ibm.com>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Christof Schmitt <cs@samba.org>