RFR: 8274168: Avoid String.compareTo == 0 to check String equality in java.management

[Andrey Turbanov]

Cleanup places, where String.compareTo is used to check String's equality.
Instead String.equals or switch expression could be used. They are faster and code is cleaner.

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Commit messages:
 - Avoid String.compareTo == 0 to check String equality

Changes: https://git.openjdk.java.net/jdk/pull/5640/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5640&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274168
  Stats: 25 lines in 2 files changed: 0 ins; 13 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5640.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5640/head:pull/5640

PR: https://git.openjdk.java.net/jdk/pull/5640