RFR: cli: use credentials for --from in git-sync

[Erik Helin]

Hi all,

please review this patch that makes sure that `git-sync` uses a username and password when fetching from the "from" repository in for case when `GIT_TOKEN` is set in the environment.

Testing:
- [x] Manual testing on Linux x64

Thanks,
Erik

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Commit messages:
 - skara-798

Changes: https://git.openjdk.java.net/skara/pull/1079/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1079&range=00
  Stats: 13 lines in 1 file changed: 13 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/1079.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1079/head:pull/1079

PR: https://git.openjdk.java.net/skara/pull/1079