mount: Simplify mnt_entry_alloc

Allocate it with xzalloc instead of massive
NULL assignment. Moreover, don't forget to
initialize @siblings.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
mount: Verify for external shared mount

If we meet shared mount point without share master belonging
to us -- it means we might fail on restore, thus require both
master/slave mount peers to be collected on dump.

In other words, the output will be like

 | (00.077025) Error (mount.c:421): Mount 49 (master_id: 2 shared_id: 0) has unreachable sharing
 | (00.077123) Error (mount.c:472): Can't proceed 4237's mountinfo
 | (00.077865) Error (namespaces.c:442): Namespaces dumping finished with error 65280

https://bugzilla.openvz.org/show_bug.cgi?id=2608

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
parasite: remove an unused id field from parasite_dump_thread

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
exec: Add support for return-arguments

Reminder: the '&<string>' arg turns out into an address in memory
containing <string>. The '@<size>' arg turns out into an address
to uninitilized memory of size <size>, which contents it printed
after syscall returns.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>