RFR: 1655: A PR/commit with an invalid jcheck config should be caught by jcheck [v5]

[Zhao Song]

> SKARA-1655 describes a problem related with invalid jcheck config in a new change.
> 
> Currently, Skara never checks if the jcheck config is changed in a new change. So for example, if we accidentally
> changed the jcheck config in a change and it was bad formatted, the bot will be in a retry loop and stuck.
> 
> In this patch, `JCheckConfCheck` is added to JCheck. If this check is configured, jcheck will check whether the jcheck config is still valid in the new change. If it is not, the specific problem will be added to the PR body and this PR will be blocked to be `ready for review`.

Zhao Song has updated the pull request incrementally with one additional commit since the last revision:

  update JCheckConfCheckTests

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

Changes:
  - all: https://git.openjdk.org/skara/pull/1415/files
  - new: https://git.openjdk.org/skara/pull/1415/files/cbf32cb4..79c073a9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1415&range=04
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1415&range=03-04

  Stats: 7 lines in 1 file changed: 1 ins; 2 del; 4 mod
  Patch: https://git.openjdk.org/skara/pull/1415.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1415/head:pull/1415

PR: https://git.openjdk.org/skara/pull/1415