RFR: JDK-8292990 Improve test coverage for XPath Axes: parent

[Bill Huang]

The goal of this task is validating the parent axis contains the parent of the context node. Context nodes include 
- root node 
- element nodes 
- text nodes 
- attribute nodes 
- namespace nodes 
- comment nodes

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Commit messages:
 - Add document root tests
 - Added relative parent tests.
 - Initial commit.

Changes: https://git.openjdk.org/jdk/pull/10107/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10107&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292990
  Stats: 160 lines in 2 files changed: 160 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10107.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10107/head:pull/10107

PR: https://git.openjdk.org/jdk/pull/10107