Quote arguments for kickstart.file.contains and
kickstart.stream.contains

Even when quoting like `kickstart.stream.contains 'debian 5.0'` it would
not work properly.

It will now.
Make kickstart infect go back to the current folder
Make kickstart.package.installed return the status

Using `&&` was making the command only return when all the packages were
installed.
Introduce kickstart.user.exec