Improve travis RL78 tests

These tests apt-get install a bunch of what seems to be unnecessary packages. I've removed a couple. @hexluthor , do we _really_ need `libncurses5:i386 zlib1g:i386` for these tests?

Also:
* I've added `|| true` so that we can fail properly if we... fail
* Only dpkg -i gnurl78 if its download succeeded