mdadm: fix segfaults when running ptests

mdadm: fix segfaults when running ptests

Currently, some segfaults are reported when running ptest:
mdadm[12333]: segfault at 0 ip 00007fe855924060 sp 00007ffc4d6caf88 error 4 in libc.so.6[7f)
Code: d2 0f 84 b7 0f 00 00 48 83 fa 01 0f 84 b9 0f 00 00 49 89 d3 89 f1 89 f8 48 83 e1 3f 4f

Backport the following upstream commits to fix them:
679bd9508a30 ("DDF: Cleanup validate_geometry_ddf_container()")
2b93288a5650 ("DDF: Fix NULL pointer dereference in validate_geometry_ddf()")
548e9b916f86 ("mdadm/Grow: Fix use after close bug by closing after fork")
9ae62977b51d ("monitor: Avoid segfault when calling NULL get_bad_blocks")

The fixes are part of the "Bug fixes and testing improvments" patchset [1].

[1] https://www.spinics.net/lists/raid/msg70621.html

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>