[jdk11u-dev] RFR: 8256202: Some tweaks for jarsigner tests PosixPermissionsTest and SymLinkTest

[Martin Doerr]

Backport of JDK-8256202. Changes in SymLinkTest.java apply cleanly.
Hunks in PosixPermissionsTest.java had to be integrated manually because the test is different in 11u (see backport of the related issues JDK-8218021 and JDK-8250968). This backport only contains cleanup in this file. Other hunks are not applicable.

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Commit messages:
 - Backport 1e9a432d59fa3fb3d038c83c88fd7eeb3052960c

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/564/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=564&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256202
  Stats: 82 lines in 2 files changed: 33 ins; 1 del; 48 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/564.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/564/head:pull/564

PR: https://git.openjdk.java.net/jdk11u-dev/pull/564