cleanup: CI checks, make lint

[metachris]

• Added CI checks (make lint and make test)
• Fixed linting errors
• Nice make output that shows all commands
• Initial cvm-proxy-server Dockerfile

Sadly, I couldn't make golangci-lint work right away, it errors with this message:

$ golangci-lint run --exclude-dirs internal
WARN [runner] Can't run linter goanalysis_metalinter: buildir: failed to load package internal: could not load export data: no export data for "github.com/google/go-tpm-tools/simulator/internal" 
ERRO Running error: can't run linter goanalysis_metalinter
buildir: failed to load package internal: could not load export data: no export data for "github.com/google/go-tpm-tools/simulator/internal" 

keeping golangci-lint for a later PR

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Output from make:

[Ruteri]

Will introduce a conflict with #8, maybe remove (the other one introduces this in some more detail)

[metachris]

good call, removed