RFR: 8328957: Update PKCS11Test.java to not use hardcoded path

[Matthew Donovan]

When resolving the location of the NSS library, the code appended a hard-coded path: `/nss/lib`. This makes it difficult for a person to specify the library when it is installed in a location such as `/usr/lib64`. 

In this PR, I removed the hard-coded path and updated the code to search the specified path for the nss library file, softokn3.

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Commit messages:
 - 8328957: Update PKCS11Test.java to not use hardcoded path

Changes: https://git.openjdk.org/jdk/pull/18488/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18488&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328957
  Stats: 18 lines in 1 file changed: 10 ins; 3 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/18488.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18488/head:pull/18488

PR: https://git.openjdk.org/jdk/pull/18488