RFR: 2049: After enabled maintainer approval in a repo, some pull requests are not updated

[Zhao Song]

Today, I enabled maintainer approval feature in openjdk/jdk8u-dev. 

After I enabled this feature, I expect to see the progress like "JDK-XXXXXXX needs maintainer approval" in the body of all open prs. 

However, this pr(https://github.com/openjdk/jdk8u-dev/pull/368) is not updated. 

The reason is that although after we enabled the maintainer approval feature, the issue labels will be calculated in the issueMetaData, there still exists some issues that doesn't contain any label. 

To solve this, I think we could add a string "approval" to issueMetaData after we enabled the maintainer approval.

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

Commit messages:
 - SKARA-2049

Changes: https://git.openjdk.org/skara/pull/1563/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1563&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2049
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/skara/pull/1563.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1563/head:pull/1563

PR: https://git.openjdk.org/skara/pull/1563