RFR: JDK-8289510 : Improve test coverage for XPath Axes: namespace

[Mahendra Chhipa]

Added tests for namespace Axis. Tests incluse namspace expressions, namespace node counts and namespace node scope.

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Commit messages:
 - JDK-8289510 : Improve test coverage for XPath Axes: namespace

Changes: https://git.openjdk.org/jdk/pull/9906/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9906&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289510
  Stats: 163 lines in 1 file changed: 163 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/9906.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9906/head:pull/9906

PR: https://git.openjdk.org/jdk/pull/9906