RFR: 295: jcheck should always use configuration from the target branch

[Erik Helin]

Hi all,

please review this patch that ensures that the bots always use the .jcheck/conf
from the target branch when checking pull requests.

Testing:
- `make test` passes on Linux x64
- Added a few new unit tests

Thanks,
Erik

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Commit messages:
 - 295: jcheck should always use configuration from the target branch

Changes: https://git.openjdk.java.net/skara/pull/491/files
 Webrev: https://webrevs.openjdk.java.net/skara/491/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-295
  Stats: 194 lines in 8 files changed: 146 ins; 15 del; 33 mod
  Patch: https://git.openjdk.java.net/skara/pull/491.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/491/head:pull/491

PR: https://git.openjdk.java.net/skara/pull/491