Keep tracefile if go binary is not found

[zbindenren]

On our servers we have the go chain not installed and servers are behind a firewall (no tunnels possible)

With this pull request it would be possible to perform a trace and copy the trace file to a system where I have the go tool chain installed. There I could run go tool trace <tracefile> and analyze the trace file with the browser.

This could maybe also solve #44.

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[zbindenren]

I signed it!

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