Bump Go versions for Travis, fix tests

[smira]

Replace gometalinter with golangci-lint.

Fix system tests (wheezy is gone, replace with stretch).

Fix linter warnings

[codecov]

Codecov Report

Merging #842 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #842      +/-   ##
==========================================
- Coverage   64.23%   64.22%   -0.01%     
==========================================
  Files          51       51              
  Lines        6514     6515       +1     
==========================================
  Hits         4184     4184              
- Misses       1825     1826       +1     
  Partials      505      505

Impacted Files	Coverage Δ
deb/remote.go	62.74% <0%> (-0.14%)	⬇️

---

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[codecov]

Codecov Report

Merging #842 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #842      +/-   ##
==========================================
- Coverage   64.23%   64.22%   -0.01%     
==========================================
  Files          51       51              
  Lines        6514     6515       +1     
==========================================
  Hits         4184     4184              
- Misses       1825     1826       +1     
  Partials      505      505

Impacted Files	Coverage Δ
s3/public.go	61.92% <ø> (ø)	⬆️
deb/deb.go	60.83% <ø> (ø)	⬆️
deb/format.go	89.23% <ø> (ø)	⬆️
deb/remote.go	62.74% <0%> (-0.14%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e2d6a53...2c91bcd. Read the comment docs.