Reduce the exported functions.

Some of them don't make sense anymore.
Set up Yum and use it to install RPMs.

We create a temporary directory where we put a temporary configuration
file and a file with all the repositories.  We'll use that one for our
basic installations.

This way we don't interfere with production Yum, nor with ncm-spma.
Simplify installation of base packages.

We can do it all with a single Yum run.  And even better, move it to
the %post phase, before any reboots.
Add a constant for a path
Turn a global variable into a constant.
Support Yum proxies when setting up Yum.
Install all relevant packages from a single function.
Remove invocations to old SPMA
Fix bugs when choosing packages to install
Install specific versions of RPM when the profile saysso
Ensure basic packages are installed exactly once
Fix bug in listing of base packages
Merge pull request #4 from piojo/aii-yum

Generate a Kickstart file that can be used with the Yum-based SPMA