refactor: add stub unit-tests to non-trivial Go packages

[smira]

This should fix code coverage calculation (code coverage should go down
significantly).

Also fixed two small issues:

1. Skip containerd tests when it can't run, this allows go test ./...
   in local mode still.

2. Silence output of go list as we aren't interested in the output, we
   run it to check that go.mod definition is complete.

Signed-off-by: Andrey Smirnov smirnov.andrey@gmail.com

[andrewrynhard]

LGTM

[codecov]

Codecov Report

Merging #556 into master will decrease coverage by 50.76%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #556       +/-   ##
==========================================
- Coverage   58.12%   7.36%   -50.77%     
==========================================
  Files           7      57       +50     
  Lines         394    3111     +2717     
==========================================
  Hits          229     229               
- Misses        133    2850     +2717     
  Partials       32      32

Impacted Files	Coverage Δ
...pp/init/pkg/system/runner/containerd/containerd.go	80.76% <0%> (ø)	⬆️
internal/pkg/chunker/stream/stream.go	0% <0%> (ø)
cmd/osctl/pkg/client/config/config.go	0% <0%> (ø)
internal/pkg/net/net.go	0% <0%> (ø)
...internal/platform/cloud/googlecloud/googlecloud.go	0% <0%> (ø)
internal/pkg/grpc/factory/factory.go	0% <0%> (ø)
internal/app/init/internal/rootfs/etc/etc.go	0% <0%> (ø)
cmd/osctl/pkg/helpers/should.go	0% <0%> (ø)
internal/pkg/install/prepare.go	0% <0%> (ø)
internal/pkg/mount/options.go	0% <0%> (ø)
... and 41 more

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