RFR: 1125: OpenJDK 7 backports incorrectly tagged with hgupdate-sync

[Erik Joelsson]

This patch makes "openjdk7u" a valid JdkVersion in the Skara version parser. This was preventing the SyncLabelBot from properly setting or removing the hgupdate-sync label on backports with this fixVersion.

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Commit messages:
 - SKARA-1125

Changes: https://git.openjdk.java.net/skara/pull/1215/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1215&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1125
  Stats: 17 lines in 3 files changed: 13 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/skara/pull/1215.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1215/head:pull/1215

PR: https://git.openjdk.java.net/skara/pull/1215