tests-util: Adding test to verify "full-string-conversion" flag

tests-util: Adding test to verify "full-string-conversion" flag

The standard string to integer conversion routines stop at the first
character which cannot be converted to a number.
However, if such a character is found, it is not considered an error.
With the flag "SMB_STR_FULL_STR_CONV" enabled, an error will be returned
if the string could not be converted entirely.

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