snap: test: add build and deploy checks

[casperdcl]

• use snapd for build-time checks
• use review-tools for pre-deploy checks

[codecov]

Codecov Report

Merging #3330 into master will increase coverage by 0.36%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3330      +/-   ##
==========================================
+ Coverage   92.47%   92.83%   +0.36%     
==========================================
  Files         140      140              
  Lines        8473     8473              
==========================================
+ Hits         7835     7866      +31     
+ Misses        638      607      -31

Impacted Files	Coverage Δ
dvc/analytics.py	96.05% <0%> (+1.31%)	⬆️
dvc/remote/ssh/connection.py	87% <0%> (+4.5%)	⬆️
dvc/system.py	87.71% <0%> (+9.64%)	⬆️
dvc/compat.py	72.22% <0%> (+55.55%)	⬆️

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