RFR: 8275185: Remove dead code and clean up jvmstat LocalVmManager [v2]

[Ioi Lam]

> LocalVmManager and PerfDataFile have APIs that are supposed to look for VMs owned by a specific user. No one uses these APIs, and they don't work anyway.
> 
> The current code is very confusing to look at. Since we're likely to change code in this area for further container support, it's better to clean up the code now.
> 
> - Remove all APIs that take a user name
> - Also removed PerfDataFile.getFile() methods that are unused
> - Cleaned up the code that looks up the hsperfdata_xxx files
>   - Fix comments to explain what's happening
>   - Avoid using Matcher.reset which is not thread-safe
>   - Renamed confusing variables such as `userFilter` to make the code more readable
>   - LocalVmManager.activeVms() probably doesn't need to be synchronized, but I kept it anyway to avoid unnecessary risks.
> 
> Testing with Oracle CI: tiers1-4, plus hs-tier5-rt (which tests containers and have extensive use of the management tools).

Ioi Lam has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into 8275185-jvmstat-LocalVmManager-cleanup-and-remove-dead-code
 - @kevinjwalls and @plummercj review - (1) restore PerfDataFile.userDirNamePattern, etc. (2) Fixed comments
 - 8275185: Remove dead code and clean up jvmstat LocalVmManager

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5923/files
  - new: https://git.openjdk.java.net/jdk/pull/5923/files/c2f3937b..bbeb7c16

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5923&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5923&range=00-01

  Stats: 43203 lines in 1054 files changed: 33107 ins; 6126 del; 3970 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5923.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5923/head:pull/5923

PR: https://git.openjdk.java.net/jdk/pull/5923