RFR: 8292297: Fix up loading of override java.security properties file

[Sean Coffey]

Ensure that security properties are only overridden if the override security properties file exists. 
Refactored some of the code in Security class initialization also.
Extra test coverage for security properties file options.

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Commit messages:
 - Merge branch 'master' into 8292297-securityConf
 - Correct URL syntax
 - fix early initization issue and expand testing
 - 8292297 initial commit

Changes: https://git.openjdk.org/jdk/pull/10251/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10251&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292297
  Stats: 165 lines in 3 files changed: 69 ins; 70 del; 26 mod
  Patch: https://git.openjdk.org/jdk/pull/10251.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10251/head:pull/10251

PR: https://git.openjdk.org/jdk/pull/10251