RFR: 41: Bot launcher should detect ev. http proxy in environment

[Erik Duveblad via github.com]

Hi all,

this patch ensures that `BotLauncher.java` correctly sets up corresponding system properties for `http_proxy`, `https_proxy` and `no_proxy`. The patch became a little larger than I intended since I had to break out `HttpProxy` into a new module and package to share it between `cli` and `bots/cli`. I also updated the Gradle `ProxyPlugin` to align with the new `proxy` module (there is unfortunately now way to use `HttpProxy` from the Gradle `ProxyPlugin`).

## Testing

- [x] Executed `sh gradlew test` successfully on Linux

Thanks,
Erik

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Commits:
 - 9584f27f:	41: Bot launcher should detect ev. http proxy in environment

Pull request:
http://git.openjdk.java.net/skara/pull/27

Webrev:
https://openjdk.github.io/cr/skara/27/webrev.00

Patch:
http://git.openjdk.java.net/skara/pull/27.diff

Fetch command:
git fetch https://github.com/openjdk/skara.git pull/27/head:pull/27