Comment 21 for bug 775124

As discussed during the installer virtual sprint, one option is to establish a size whereby disks smaller than this should automatically override the space check, provided that they have enough space (plus a small amount) for the contents of the installation.

The rationale was that if a disk is smaller than the minimum size check but still large enough to hold the installation, we shouldn't get in the users way, provided that attempting the install wont hit -ENOSPC.