cleanup: changed match to if let in CreateDir and RemoveDir

Changed `return match { Ok(_) => no_error_code, err => err }`
to `if let Err(err) { return Err(err) }; no_error_code`
This may be less idiomatic (not sure) but is much nicer to read and
understand (at least to me)
2 jobs for master in 2 minutes and 24 seconds (queued for 2 seconds)
Name Stage Failure
style:check Test
- }).map(Box::new)
+ })
+ .map(Box::new)
.map(|b| b as Box<Command>)
ModifySlice {
ERROR: Job failed: exit status 1