RFR: exracting method to fill in result status to allow for overriding in implementations of Script

[andrlos]

This is an alternative approach to https://github.com/openjdk/jtharness/pull/57
counting on Script subclasses that will allow for such modifications.

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Commit messages:
 - exracting method to fill in result status to allow for overriding in implementations of Script

Changes: https://git.openjdk.org/jtharness/pull/59/files
 Webrev: https://webrevs.openjdk.org/?repo=jtharness&pr=59&range=00
  Stats: 12 lines in 1 file changed: 11 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtharness/pull/59.diff
  Fetch: git fetch https://git.openjdk.org/jtharness.git pull/59/head:pull/59

PR: https://git.openjdk.org/jtharness/pull/59