RFR: 8270380: Change the default value of the java.security.manager system property to disallow [v2]

[Weijun Wang]

> This change modifies the default value of the `java.security.manager` system property from "allow" to "disallow". This means unless it's explicitly set to "allow", any call to `System.setSecurityManager()` would throw an UOE.
> 
> The `AllowSecurityManager.java` and `SecurityManagerWarnings.java` tests are updated to confirm this behavior change. Two other tests are updated because they were added after JDK-8267184 and do not have `-Djava.security.manager=allow` on its `@run` line even it they need to install a `SecurityManager` at runtime.
> 
> Please note that this code change requires jtreg to be upgraded to 6.1, where a security manager [will not be set](https://bugs.openjdk.java.net/browse/CODETOOLS-7902990).

Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:

  sections etc

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5204/files
  - new: https://git.openjdk.java.net/jdk/pull/5204/files/63b1b7c9..08635b91

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5204&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5204&range=00-01

  Stats: 7 lines in 2 files changed: 2 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5204.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5204/head:pull/5204

PR: https://git.openjdk.java.net/jdk/pull/5204