Shell scripts compatibility enhancements

[javornikolov]

Here are some changes in attempt to make the setup shell scripts more portable (in particular - compatible with Ubuntu 13.10).

• Use . instead of source to load vars.sh. Seems source is not POSIX compatible. (In particular - it's not part of dash shell which is the default shell mapped to /bin/bash in recent versions of Debian and Ubuntu). (Another alternative would be to explicitly require some other shell like bash or zsh instead of sh)
• Parameterize some parts of the variables: to allow easier override. (E.g. - my vbox dir is located elsewhere)
• Add some up-front checks of isos and boxes dir existence to avoid having partially configured vbox VMs.

[casr]

Wow! I've got a pretty busy week ahead but I'll try and look this over on the weekend.

Thanks for the contribution!

[casr]

I think from reviewing some of the commits here and some of the other forks it would be worth thinking about a different command structure. I don't want to overburden the repo with loads of small script files when it might be simpler to have a single entry point and pass command line parameters (which could override the defaults in vars.sh in the common cases). I'll open a separate issue for that.

On other fronts, I'm all for having a more cross-platform script so thanks for making me consider those cases more.
Automatic creation of the output directories is a nice addition too which I had glossed over when I threw this together initially :) . I'll try and integrate those changes ASAP.

[casr]

• I've combined a6a062e, 6d4fd8b and 3b7dde4 as they all did the same kind of thing (or undid it). Their new ref is cd94ebf.
• 9de8cf0 I will delay for now and resolve it with Unified script command #12.
• 21aa454 great; don't foresee a problem with that. New ref 34b8bd9.
• 994f298 seems to go against the intention of 3b7dde4 but I think it the overall idea should remain. I'll sort that later.
• The parameterisation stuff I'll hold off for now. Again that might tie in with Unified script command #12.

(Side note: I like commit messages to be formatted like git manual guidelines with a short < 50 character first line message. So I've gone ahead and reworded the commits)

Cheers for the PR!

[javornikolov]

OK, cool.

994f298 seems to go against the intention of 3b7dde4 but I think it the overall idea should remain.

Yes, the commit is opposite of the other's intention. The second change was with the idea be able to run scripts from other directory with a local customized vars.sh.