MFC r330295: ZFS: fix adding vdevs to very large pools

PR: 226096

MFC r323791: MFV r323790: 8567 Inconsistent return value in zpool_read_label

MFC r305206: MFV r302658:
6872 zfs libraries should not allow uninitialized variables

illumos/illumos-gate@f83b46baf98d276f5f84fa84c8b461f412ac1f5e
https://github.com/illumos/illumos-gate/commit/f83b46baf98d276f5f84fa84c8b461f41
2ac1f5e

https://www.illumos.org/issues/6872
We compile the zfs libraries with -Wno-uninitialized. We should remove
this. Change makefiles, fix new warnings, fix pbchk errors.

Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Paul Dagnelie <pcd@delphix.com>

MFC r297763: MFV r297760: 6418 zpool should have a label clearing command

Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Author: Will Andrews <will@firepipe.net>

Closes #83
Closes #32

openzfs/openzfs@9663688425131744221ea99f9e66b9ed964492ae

FreeBSD already had `zpool labelclear` functionality, so this is mostly
just a diff reduction.

MFC r296528: MFV r296527: 6659 nvlist_free(NULL) is a no-op

Reviewed by: Toomas Soome <tsoome@me.com>
Reviewed by: Marcel Telka <marcel@telka.sk>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>

illumos/illumos-gate@aab83bb83be7342f6cfccaed8d5fe0b2f404855d

MFC r277300 (by smh): Mechanically convert cddl sun #ifdef's to illumos

Since the upstream for cddl code is now illumos not sun, mechanically
convert all sun #ifdef's to illumos #ifdef's which have been used in all
newer code for some time.

Also do a manual pass to correct the use if #ifdef comments as per style(9)
as well as few uses of #if defined(__FreeBSD__) vs #ifndef illumos.

MFC r284308: MFV r284042: 1778 Assertion failed: rn->rn_nozpool == B_FALSE

MFC r277433: MFV r277432:

Plug various memory leaks in libzfs import implementation.

Illumos issue:
5518 Memory leaks in libzfs import implementation

MFC r271527: MFV r271511:

Use fnvlist_* to make code more readable.

Illumos issue:
5135 zpool_find_import_cached() can use fnvlist_*

Approved by: re (gjb)

MFC r265821:
Comment out some pointless device open/close around reading device IDs.

FreeBSD ZFS port unlike OpenSolaris does not use device IDs, and does not
implement respective devid_*() fuctions. It is pointless to open devices
just to close them back immediately.

MFC r262577: MFV r262570:

4626 libzfs memleak in zpool_in_use()

MFC r259168:
Don't even try to read vdev labels from devices smaller then SPA_MINDEVSIZE
(64MB). Even if we would find one somehow, ZFS kernel code rejects such
devices. It is funny to look on attempts to read 4 256K vdev labels from
1.44MB floppy, though it is not very practical and quite slow.

MFC r284308: MFV r284042: 1778 Assertion failed: rn->rn_nozpool == B_FALSE

MFC r277433: MFV r277432:

Plug various memory leaks in libzfs import implementation.

Illumos issue:
5518 Memory leaks in libzfs import implementation

MFC r271527: MFV r271511:

Use fnvlist_* to make code more readable.

Illumos issue:
5135 zpool_find_import_cached() can use fnvlist_*

Approved by: re (gjb)

MFC r265821:
Comment out some pointless device open/close around reading device IDs.

FreeBSD ZFS port unlike OpenSolaris does not use device IDs, and does not
implement respective devid_*() fuctions. It is pointless to open devices
just to close them back immediately.

MFC r262577: MFV r262570:

4626 libzfs memleak in zpool_in_use()

MFC r259168:
Don't even try to read vdev labels from devices smaller then SPA_MINDEVSIZE
(64MB). Even if we would find one somehow, ZFS kernel code rejects such
devices. It is funny to look on attempts to read 4 256K vdev labels from
1.44MB floppy, though it is not very practical and quite slow.