man/*: always use EXIT STATUS to describe, well, exit status

Previous commit aa3258e2426f unified the header of this section to be
DIAGNOSTICS. While unification was a good thing, name was badly chosen,
since DIAGNOSTICS is for various error messages printed by a program etc.,

The proper name is EXIT STATUS.

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
14 files changed