This test tests the following combinations:

1. parent and child have a cow-ed mapping
2. parent and child have just coinciding mappings

the pages state in both should be in all possible combinations of

 a. write mapped
 b. read mapped
 c. not touched
 d. before fork
 e. after fork

v2: * wait until a child are not prepared
    * check a FILE | PRIVATE mappings
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>