TESTS: drop explicit quotes from empty command line arguments

TESTS: drop explicit quotes from empty command line arguments

Depending on circumstances, something like this:

    ok(run(app(['openssl', 'whatever', '-config', '""', ...])))

might end up with a command like this:

    ./util/wrap.pl apps/openssl whatever -config '""'

Simply use an empty string (i.e. '' instead of '""') and let the
command line fixup functions do their job.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15822)