RFR: 8304438: jcmd JVMTI.agent_load should obey EnableDynamicAgentLoading

[Serguei Spitsyn]

The VM option EnableDynamicAgentLoading was added in JDK 9, default true, to allow deployment to choose whether to allow agents to be loaded/started in the VM. The VM option does the right thing for tools using the Attach API but jcmd JVMTI.agent_load was missed. This should be fixed to disallow loading JVMTI agents when the EnableDynamicAgentLoading is false.

Testing:
 - run new test `test/jdk/sun/tools/jcmd/TestJcmdNoAgentLoad.java`
 - TBD: submit mach5 tiers 1-5 to make sure no new regressions are introduced

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Commit messages:
 - 8304438: jcmd JVMTI.agent_load should obey EnableDynamicAgentLoading

Changes: https://git.openjdk.org/jdk/pull/14244/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14244&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304438
  Stats: 78 lines in 2 files changed: 78 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14244.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14244/head:pull/14244

PR: https://git.openjdk.org/jdk/pull/14244