zdtm: add transition test for memory

This test does a few operation in a loop
* create a mapping with random flags
* touch a few pages in a new mapping, if it's writable

This test has two processes. The second process goes a predefined value
of steps behind the first one. When we need to check the result, we stop
the first process, wait until the second process come to the same point
and compare these processes. The processes are dumped in different
states, but at the end both processes must be in the same state.

bash -x test/zdtm.sh -s -i 5 -r transition/maps007
...
(00.743662) Error (page-read.c:107): Missing 139773474525184 in parent pagemap, current iov: base=7f1f8c4cf000,len=4096
(00.743696) Error (page-xfer.c:523): Hole 0x7f1f8c4c5000/4096 not found in parent
(00.744196) Error (mem.c:331): Can't dump page with parasite
(00.758201) Error (cr-dump.c:1828): Dumping FAILED.

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