fix(check_live_ram): increase /run tmpfs size if needed

[FGrose]

fix(check_live_ram): increase /run tmpfs size, if needed

Check the size and available space in /run to enlarge it,
  if needed.
Introduce the check_meminfo() function to dracut-lib.sh
  to replace a less versatile sed call.
Also, use local variables,
  use parameter expansion to assign a default value,
  use test exit logic directly, where possible,
  tweak comments,
  and move the check_live_ram() function to img-lib.sh.

Checklist

• [✔] I have tested it locally

Fixes #2550

[LaszloGombos]

This looks good to me.

@FGrose what do you think about moving check_live_ram (and check_meminfo) to img-lib.sh instead of the catch-all dracut-lib.sh ?

[stale]

This issue is being marked as stale because it has not had any recent activity. It will be closed if no further activity occurs. If this is still an issue in the latest release of Dracut and you would like to keep it open please comment on this issue within the next 7 days. Thank you for your contributions.

[cbs228]

This PR is needed for #2550 and is still waiting on review.

[Athwale]

Any progress on this please, can someone review this and approve it? I am hitting this problem on f39.
Thanks.

[Conan-Kudo]

I approved it, but I haven't had merge permissions for a while. ☹️

[Athwale]

@haraldh @johannbg @tblume Can you please have a look at this? Thank you.

[Athwale]

This is a related issue also connected to the low /run size
#2550
Particularly the rd.writable.fsimg=1 copies rootfs.img into RAM and this image is typically even larger than the squashfs.img.