man/vzctl.8: add/describe 'vzquota on failed' exit code (60)

After commits d75908d0 and 84f9ab9329 vzctl may now exit with
VZ_DQ_ON (60) exit code, which means 'vzquota on failed'.
Document it.

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
1 file changed