Move vagrant user's username into variables.

This makes it easier to use the prepare_iso.sh script to set up an ISO with
a different username and password, allowing it to be used to provision
non-vagrant images.
Remove explicit mention of vagrant in comments.
Include useful script to generate a shadowhash file.
Add optional command line switches to prepare_iso.sh.

prepare_iso.sh now accepts three optional command line switches to modify the
user, password and image of the root user in the prepared image.
Point to the correct vagrant.jpg path.
Fix username template in sudoers file.
Include vagrant.jpg.
Extract vagrant settings into user variables.

The defaults still build a vagrant compatible image as before, but now there
are variables to configure the username, password, whether the user is
automatically logged in, and whether the vagrant SSH keys are installed.
Merge branch 'master' into easier-renaming-of-vagrant-user
Use user variables in parallels builder.
Update README.md
Rename user variables.
Set parallels tools path dynamically.
Remove unused kcpassword file.
Document set_kcpassword.py.
Merge branch 'master' into easier-renaming-of-vagrant-user

Conflicts:
	prepare_iso/support/pkg-postinstall
Default autologin to false.
Document prepare_iso.sh switches.
Document new packer variables.
Merge pull request #23 from newspaperclub/easier-renaming-of-vagrant-user

Move vagrant user's username into variables.