dracut-module-setup.sh: check whether to include multipath-hostonly or not

Due to the following commit in dracut, which splits out hostonly modules
commit 5ce7cc7337a4c769b223152c083914f2052aa348
Author: Harald Hoyer <harald@redhat.com>
Date:   Mon Jul 10 13:28:40 2017 +0200

    add 90multipath-hostonly module

    hardcoding the wwid of the drives in the initramfs causes problems
    when the drives are cloned to a system with the same hardware, but
    different disk wwid's

    https://bugzilla.redhat.com/show_bug.cgi?id=1457311

So kdump should decide whether to include the hostonly module.
The multipath-hostonly can help kdump to include only the needed mpath device,
in order to use less memory by 2nd kernel.

---- The performance -----
before this patch
[root@localhost ~]# time kdumpctl start
Detected change(s) in the following file(s):

  /etc/kdump.conf
Rebuilding /boot/initramfs-4.13.9-300.fc27.x86_64kdump.img
kexec: loaded kdump kernel
Starting kdump: [OK]

real    0m12.485s
user    0m10.096s
sys     0m1.887s

after this patch

root@localhost ~]# time kdumpctl start
Detected change(s) in the following file(s):

  /etc/kdump.conf
Rebuilding /boot/initramfs-4.13.9-300.fc27.x86_64kdump.img
kexec: loaded kdump kernel
Starting kdump: [OK]

real    0m15.839s
user    0m13.015s
sys     0m1.853s

Signed-off-by: Pingfan Liu <piliu@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>

dracut-module-setup.sh

@@ -7,6 +7,13 @@ if ! [[ -d "${initdir}/tmp" ]]; then
     mkdir -p "${initdir}/tmp"
 fi
 
+is_mpath() {
+    local _dev=$1
+    [ -e /sys/dev/block/$_dev/dm/uuid ] || return 1
+    [[ $(cat /sys/dev/block/$_dev/dm/uuid) =~ mpath- ]] && return 0
+    return 1
+}
+
 check() {
     [[ $debug ]] && set -x
     #kdumpctl sets this explicitly
@@ -28,6 +35,7 @@ depends() {
         _dep="$_dep network"
     fi
 
+    for_each_host_dev_and_slaves is_mpath && _dep="$_dep multipath-hostonly"
     echo $_dep
     return 0
 }