zdtm: Use "post-dump" script for "-d" and "-s" option

v2:
 - Use special opcode 32 to distinguish error cases
 - Use --scripts for snapshot testings
v3:
 - test for both 32 and 0 for error code
v4: (by avagin@)
 - restore from the last snapshot
v5:
 - update comment

https://bugzilla.openvz.org/show_bug.cgi?id=2583



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