RFR: 245: CLI tools do not consider git's http.proxy configuration

[Erik Helin]

Hi all,

please review this patch that makes the CLI tools respect git's
[http.proxy](https://git-scm.com/docs/git-config#Documentation/git-config.txt-httpproxy)
setting. The behavior with this patch is if `http_proxy`, `https_proxy` and/or
`no_proxy` is *not* set, then we try to set the proxy based on git's
`http.proxy` config (i.e. `http_proxy` and friends have precedence).

Thanks,
Erik

## Testing
- [x] Manual testing of CLI tools behind http(s) proxy

-------------

Commits:
 - 8ba31022: Support git's http.proxy in HttpProxy

Changes: https://git.openjdk.java.net/skara/pull/379/files
 Webrev: https://webrevs.openjdk.java.net/skara/379/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-245
  Stats: 50 lines in 1 file changed: 44 ins; 2 del; 4 mod
  Patch: https://git.openjdk.java.net/skara/pull/379.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/379/head:pull/379

PR: https://git.openjdk.java.net/skara/pull/379