The DiskBuilder class is able to build a disk its corresponding
format and the installation image to install this disk by using
the InstallImageBuilder. However all three tasks were handled
in a row which lead to the problem that resources like active
mount processes were still open when e.g the disk format is
created. The race conditions produced here lead to an undefined
state of the resulting disk format and/or install image. In
order to avoid this the DiskBuilder class has been refactored
in a way that each tasks is an atomic operation which is
freeing its resources after success
