fakeroot: disable capabilities

These don't autodetect consistently and are process rather than file
capabilities, so not very useful in the buildroot context.
Otherwise we'd have to unconditionally pull host-libcap (or fix the
detection, but again, not useful so there's no need).

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>