Improve mkinitrd procedure

[Moises Henriquez]

The current code for creating the initrd upon install should be modified. The current setup has a hard-coded list of modules we load with the initrd, and the / partition is passed as an argument. This works, but the results are not reproducible afterwards on the installed system.

Here is the suggested approach

Make the installer write out an /etc/mkinitrd.conf file with the parameters given during installation for the / partition. The kernel version can be passed as an argument when the installer runs the mkinitrd command, but should default to $(uname -r).

As a result of this, the mkinitrd method of the installer should be reduced to only calling the mkinitrd command and passing the path to mkinitrd.conf to it. Doing this will allow us to re-build this initrd after the system has been installed, and if the user needs to change the initrd in some way, ie, adding or removing included modules, disabling splash, etc, we can just instruct them to modify their mkinitrd.conf and run the mkinitrd command