Set zstd as the default compression method for kdump initrd
    
    resolves: bz1896698
    upstream: fedora
    conflict: none
    
    commit 0311f6e25bec9994de2c6b156b5a568583aa8aae
    Author: Tao Liu <ltao@redhat.com>
    Date:   Wed Jan 5 17:42:12 2022 +0800
    
        Set zstd as the default compression method for kdump initrd
    
        zstd has better compression ratio and time consumption balance.
        When no customized compression method specified in kdump.conf,
        we will use zstd as the default compression method.
    
        **The test method:
    
        I installed kexec-tools with and without the patch, executing the following
        command for 4 times, and calculate the averange time:
    
        $ rm -f /boot/initramfs-*kdump.img && time kdumpctl rebuild && \
          ls -ail /boot/initramfs-*kdump.img
    
        **The test result:
    
        Bare metal x86_64 machine:
                dracut with squash module
                 zlib     lzo      xz       lz4        zstd
        real     10.6282  11.0398  11.395   8.6424    10.1676
        user      9.8932  11.9072  14.2304  2.8286     8.6468
        sys       3.523    3.4626   3.6028  3.5        3.4942
        size of
        kdump.img 30575616 31419392 27102208 36666368 29236224
    
                dracut without squash module
                zlib      lzo      xz       lz4        zstd
        real     9.509    19.4876  11.6724  9.0338    10.267
        user    10.6028   14.516   17.8662  4.0476     9.0936
        sys      2.942     2.9184   3.0662  2.9232     3.0662
        size of
        kdump.img 19247949 19958120 14505056 21112544 17007764
    
        PowerVM hosted ppc64le VM:
                dracut with squash module | dracut without sqaush module
                 zlib        zstd         |  zlib          zstd
        real     10.6742     10.7572      |   9.7676       10.5722
        user     18.754      19.8338      |  20.7932       13.179
        sys       1.8358      1.864       |   1.637         1.663
                                          |
        size of                           |
        kdump.img 36917248   35467264     |  21441323      19007108
    
        **discussion
    
        zstd has a better compression ratio and time consumption balance.
    
        Acked-by: Coiby Xu <coxu@redhat.com>
        Signed-off-by: Tao Liu <ltao@redhat.com>
    
    Signed-off-by: Tao Liu <ltao@redhat.com>