RFR: 1737: Draft PR for clean backport mistakenly marked as ready

[Zhao Song]

1. readyForIntegration for normal pr is determined by 
(1) whether there is any failed check 
(2) whether there is any additional errors 
(3) whether there is any uncompleted additional progress 
(4) whether there is any integration blocker 

So if there is a draft normal pr, there will always exist a failed check(ReviewersCheck will always fail because the pr is in draft mode and nobody will approve this pr) 
Therefore, a draft normal pr will not be marked as 'ready' because there is a failed check not because this pr is in draft mode. 

2. readyForIntegration for clean backport is determined by 
(1) whether this pr is ready for review(TooFewReviewersIssue won't make it false) 
(2) whether there is any additional errors 
(3) whether there is any uncompleted additional progress 
(4) whether there is any integration blocker 

So if there is a draft clean backport pr, readyForIntegration will be true in most cases. 
Therefore, the clean backport pr will be marked as 'ready' whether it is in draft mode or not.

In this patch, whether there is an rfr label will determine whether readyforintegration is true or false.

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Commit messages:
 - SKARA-1737

Changes: https://git.openjdk.org/skara/pull/1456/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1456&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1737
  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/skara/pull/1456.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1456/head:pull/1456

PR: https://git.openjdk.org/skara/pull/1456