tree-wide: Use "unmet" for condition checks, not "failed"

tree-wide: Use "unmet" for condition checks, not "failed"

Often I end up debugging a problem on a system, and I
do e.g. `journalctl --grep=failed|error`.  The use of the term
"failed" for condition checks adds a *lot* of unnecessary noise into
this.

Now, I know this regexp search isn't precise, but it has proven
to be useful to me.

I think "failed" is too strong of a term as a baseline, and also
just stands out to e.g. humans watching their servers boot or
whatever.

The term "met condition" is fairly widely used, e.g.
https://stackoverflow.com/questions/63751794/what-does-the-condition-is-met-exactly-mean-in-programming-languages

Use that instead.