This confirms that the fix to handle dumpable flag set to 2 still works after
restore.

To force dumpable flag set to 0 or 2 (whatever the fs.suid_dumpable is set to),
chmod the test binary to 0111 (executable, but not readable) and execv() it
while running as non-root.  The kernel will unset the dumpable flag to prevent
a core dump or ptrace to giving the user access to the pages of the binary
(which are supposedly not readable by that user.)

Tested:
- # test/zdtm.sh static/dumpable02
  Test: zdtm/live/static/dumpable02, Result: PASS
- # test/zdtm.sh ns/static/dumpable02
  Test: zdtm/live/static/dumpable02, Result: PASS
- Used -DDEBUG to confirm the value of the dumpable flag was 0 or 2 to match
  the fs.suid_dumpable sysctl in the tests (both in and out of namespaces.)
- Confirmed that the test fails if the commit that fixes handling of dumpable
  flag with value 2 is reverted and the fs.suid_dumpable sysctl is set to 2.
Signed-off-by: Filipe Brandenburger <filbranden@google.com>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>