[Bug 1800566] [NEW] Make reset_devices parameter default for kdump and decouple kdump systemd service from the KDUMP_CMDLINE_APPEND

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[Impact]

* Kdump does not configure by default the crash kernel to perform a
device reset by default, by passing the "reset_devices" parameter. Also,
the systemd service "kdump-tools-dump" is tightly-coupled with
KDUMP_CMDLINE_APPEND and it shouldn't, to prevent user confusion.

* Kernel has the "reset_devices" parameter that drivers can opt-in, and
perform special activity in case this parameter is parsed from command-
line. For example, in kdump kernels it hints the drivers that they are
booting from a non-healthy condition and needs to issue some form of
reset to the adapter, like clearing DMA mapping in their firmware for
example. Users currently (kernel v5.2) are: aacraid, hpsa, ipr,
megaraid_sas, mpt3sas, smartpqi, xenbus.

This should be enabled by default in the kdump config file to be added
in the kdump kernel command-line for all versions.

* The systemd service"kdump-tools-dump" is responsible for triggering the execution of the makedumpfile tool ultimately. Kdump from Xenial+ releases rely on systemd as their init system, so this service is the way to trigger the kdump mechanism. Currently it is configured as any other parameter in KDUMP_CMDLINE_APPEND, meaning if user decides to change the line they need to remember adding the systemd service back. It's not really a parameter that should be easily manipulated in kdump line, since there's no use for it except to instruct systemd to load kdump; the only 
reasonable case for removing it is to debug kdump itself.


[Test Case]

1) Deploy a Disco VM e.g. with uvt-kvm
2) Install the kdump-tools package
3) Run `kdump-config test`and check for the 'reset_devices' parameter:

$ kdump-config test
...
kexec command to be used:
  /sbin/kexec -p --command-line="BOOT_IMAGE=/boot/vmlinuz-4.15.0-45-generic root=LABEL=cloudimg-rootfs ro console=tty1 console=ttyS0 nr_cpus=1 systemd.unit=kdump-tools.service irqpoll nousb ata_piix.prefer_ms_hyperv=0" /var/lib/kdump/vmlinuz

Also, by changing the KDUMP_CMDLINE_APPEND we can see "systemd.unit
=kdump-tools.service" to be removed.


[Regression Potential]

The regression potential is low, since it doesn't need any changes in
makedumpfile code and we're only adding a parameter on the crash kernel
command-line. The risks are related with bad behavior with the kernel
when using "reset_devices", like if the driver has bugs in this path.
It's considered safer to have the option (and this way prevent problems
for booting a unhealthy kernel with potential stuck DMAs in the devices)
than not having it.

Regarding the other change, about the systemd service, it'll only affect
users the are debugging kdump itself and it has no known regression
potential.

** Affects: makedumpfile (Ubuntu)
     Importance: High
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: In Progress

** Affects: makedumpfile (Ubuntu Trusty)
     Importance: High
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Won't Fix

** Affects: makedumpfile (Ubuntu Xenial)
     Importance: High
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Confirmed

** Affects: makedumpfile (Ubuntu Bionic)
     Importance: High
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Confirmed

** Affects: makedumpfile (Ubuntu Cosmic)
     Importance: High
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Confirmed

** Affects: makedumpfile (Ubuntu Disco)
     Importance: High
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: Confirmed

** Affects: makedumpfile (Ubuntu Eoan)
     Importance: High
     Assignee: Guilherme G. Piccoli (gpiccoli)
         Status: In Progress


** Tags: patch seg
-- 
Make reset_devices parameter default for kdump and decouple kdump systemd service from the KDUMP_CMDLINE_APPEND
https://bugs.launchpad.net/bugs/1800566
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