Stop verifying opcode results in dry_run mode

Commit 1ce03fb1 (“Add ht-based result checks to opcodes”) introduced
infrastructure for checking opcode results, and subsequent commits
improved the list of opcodes which do declare a result, however this
was not tested for dry-run mode operation.

Furthermore, there's no authoritative list of which opcode/LUs support
dry_run mode at all; currently, this is based/restricted on the list
of CLI options, so… for now we disable the result verification if the
opcode has been executed in dry_run mode.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>