Only clean up pod filesystems if umount succeeds

[brandond]

Proposed Changes

Only clean up pod filesystems if umount succeeds.

If the unmount fails for some reason we shouldn't rm -rf the mountpoint, there might still be stuff under it.

Types of Changes

killall script; bugfix

Verification

See linked issue

Testing

Linked Issues

• rke2 start fails after rke2-killall.sh execution #6571 (comment)

User-Facing Change

Further Comments

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 16.62%. Comparing base (26e1146) to head (9c7029d).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7134   +/-   ##
=======================================
  Coverage   16.62%   16.62%           
=======================================
  Files          32       32           
  Lines        3423     3423           
=======================================
  Hits          569      569           
  Misses       2812     2812           
  Partials       42       42           

Flag	Coverage Δ
unittests	16.62% <ø> (ø)

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[brandond]

I will note that we do the same thing much more concisely in k3s, although it requires xargs which we have so far avoided requiring for RKE2.

https://github.com/k3s-io/k3s/blob/v1.31.1%2Bk3s1/install.sh#L839-L845