vzctl set --devices: made cumulative, fix

This is the same as commits 90e8dd6 and b8708e2 for vzctl set
--devnodes. From now on:

* the option is now cumulative, so any new devices set by
  "vzctl set --devices" command are added to the existing devices

* vzctl set --devices t:major:minor:none --save" removes the device
  from the configuration.

Note if last device is deleted from the list, we have to add DEVICES=""
to the configuration file (see explanation in commit b8708e2).

Related to https://bugzilla.openvz.org/3186

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