RFR: 8292848: AWT_Mixing and TrayIcon tests fail on el8 with hard-coded isOel7

[KIRIYAMA Takuya]

Could you please review the JDK-8292848 bug fixes?
The purpose of the isOel7 method is to detect differences in GNOME version changes, and the isOel7 
result should be true after version 8.
I modified the isOel7 method to use regular expressions instead of hard-coded versions to be able to 
detect the new os version.
I also changed the method name to match the new conditions.

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Commit messages:
 - 8292848: AWT_Mixing and TrayIcon tests fail on el8 with hard-coded isOel7
 - 8292848: AWT_Mixing and TrayIcon tests fail on el8 with hard-coded isOel7

Changes: https://git.openjdk.org/jdk/pull/9995/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9995&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292848
  Stats: 69 lines in 12 files changed: 19 ins; 0 del; 50 mod
  Patch: https://git.openjdk.org/jdk/pull/9995.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9995/head:pull/9995

PR: https://git.openjdk.org/jdk/pull/9995