move SSH file atomically

[rberrelleza]

I think this should help with the ssh config corruption issue we've seen every now and then.
Signed-off-by: Ramiro Berrelleza rberrelleza@gmail.com

[codecov]

Codecov Report

Merging #773 into master will decrease coverage by 0.03%.
The diff coverage is 18.18%.

@@            Coverage Diff             @@
##           master     #773      +/-   ##
==========================================
- Coverage   31.98%   31.95%   -0.04%     
==========================================
  Files          62       62              
  Lines        4821     4829       +8     
==========================================
+ Hits         1542     1543       +1     
- Misses       3160     3165       +5     
- Partials      119      121       +2

Impacted Files	Coverage Δ
pkg/ssh/ssh.go	74.19% <0%> (ø)	⬆️
cmd/up.go	0% <0%> (ø)	⬆️
pkg/ssh/config.go	74.24% <23.52%> (-2.75%)	⬇️

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[derek]

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