In addition, file-system tests will use the AHCI driver instead of the
ATAPI driver. This change side-steps certain issues with Qemu's IDE
emulation.
Fixes#942.
The old variant provided 8K capability slots to all processes on core,
which increased binaries by 180 KB for the static allocator. I reduced it
to 4K capabilities stay under 100 KB overhead for the allocator.
Anyway, pci_drv and pl11x_drv need more RAM quota now: 2M for pl11x_drv
and 1M for pci_drv.