RFR: 8171508: os::jvm_path: error in handling -Dsun.java.launcher.is_altjvm option after 8066474

[Calvin Cheung]

This change fixes two issues in `os::jvm_path()`:

- go back 4 instead of 5 slashes and then checking for "/jre/lib";
- fix the hardcoded "hotspot" sub-directory before the jvm library name.

Passed tiers 1 - 3 testing.

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Commit messages:
 - 8171508: os::jvm_path: error in handling -Dsun.java.launcher.is_altjvm option after 8066474

Changes: https://git.openjdk.org/jdk/pull/24310/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24310&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8171508
  Stats: 21 lines in 4 files changed: 3 ins; 4 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/24310.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24310/head:pull/24310

PR: https://git.openjdk.org/jdk/pull/24310