libct: API call for detaching from ct handler

For local session this is now equivalent to destroying. In
the future we might think about vzctl-like CT management
when container lives by its own and we can open/detach its
handle.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
fs: Allow to switch fs private type when CT is stopped

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
util: Helper for bind-mounting paths

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
veth: Factor out veth conf freeing

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
net: Add API call for removing nets from configuration

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
fs: Add API call for removing external bind mounts

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
make: Fix deps on protobuf for libct

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>