OpenSSL::Test: add a statusvar option for run with capture => 1

When using run() with capture => 1, there was no way to find out if
the command was successful or not.  This change adds a statusvar
option, that must refer to a scalar variable, for example:

    my $status = undef;
    my @line = run(["whatever"], capture => 1, statusvar => \$status);

$status will be 1 if the command "whatever" was successful, 0
otherwise.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3004)