md5/tests: extend md5 test

The testloop function is called with various parameters, but those
were ignored in the coreutils-c-test script. This was an oversight
and is fixed by passing the option to all invocations of the hash
functions in this test script.

Reported by: des
MFC after: 3 days

(cherry picked from commit d804497068c16bcb05383d7227d899f4ba59f706)