Add Linux kmemleak support to ZTS
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Description

Add Linux kmemleak support to ZTS

Kmemleak clear is invoked right before every test case run.
Kmemleak scan is requested right after each test case is finished.
Kmemleak instrumentation is not used for setup/cleanup/pretest/posttest/failsafe stages to shorten the test case execution time.
Kmemleak periodic scan is disabled (scan=0) before the test suite run to avoid interfering with the on-demand scan results.
There are unavoidable potential false positives coming from kernel areas other than OpenZFS module.
The ZTS with kmemleak enabled duration is increased by ~50%.

Example run

Running Time:   07:12:13
Percent passed: 98.3%

unreferenced object 0xffff9da82aea5410 (size 80):
  comm "kworker/u32:10", pid 942206, jiffies 4296749716 (age 2615.516s)
  hex dump (first 32 bytes):
    00 30 30 00 00 00 00 00 ff 8f 30 00 00 00 00 00  .00.......0.....
    51 e6 77 05 a8 9d ff ff 00 00 00 00 00 00 00 00  Q.w.............
  backtrace:
    [<000000005cf1fea2>] alloc_extent_state+0x1d/0xb0 [btrfs]
    [<0000000083f78ae5>] set_extent_bit+0x2ff/0x670 [btrfs]
    [<00000000de29249e>] lock_extent_bits+0x6b/0xa0 [btrfs]
    [<00000000b241f424>] lock_and_cleanup_extent_if_need+0xaf/0x1c0
       [btrfs]
    [<0000000093ca72b5>] btrfs_buffered_write+0x297/0x7d0 [btrfs]
    [<000000002c2938c8>] btrfs_file_write_iter+0x127/0x390 [btrfs]
    [<00000000b888f720>] do_iter_readv_writev+0x152/0x1b0
    [<00000000320f0bcc>] do_iter_write+0x7c/0x1c0
    [<000000000b5a8fe0>] lo_write_bvec+0x62/0x150 [loop]
    [<000000009aa03c73>] loop_process_work+0x250/0xbd0 [loop]
    [<00000000c7487d8a>] process_one_work+0x1f1/0x390
    [<000000000b236831>] worker_thread+0x53/0x3e0
    [<0000000023cb3e57>] kthread+0x127/0x150
    [<000000002d48676a>] ret_from_fork+0x22/0x30

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: szubersk <szuberskidamian@gmail.com>
Closes #13084