RFR: 1011: Allow JDK fixVersion to be XXu-cpu

[Erik Joelsson]

We would like to be able to use fixVersions in JBS on the form "16u-cpu". This PR contains the necessary changes needed to the JdkVersion class to handle such versions. I'm also adding test cases to verify that it behaves as we want it.

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Commit messages:
 - SKARA-1011

Changes: https://git.openjdk.java.net/skara/pull/1144/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1144&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1011
  Stats: 48 lines in 3 files changed: 46 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/1144.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1144/head:pull/1144

PR: https://git.openjdk.java.net/skara/pull/1144