Handle Shutdown via TERM gracefully

The wildfly server currently terminates immediately performs a standard (non-graceful) shutdown in response to a TERM signal. To achieve a clean graceful shutdown requires invoking the CLI tooling. This is particularly problematic in container environments like kubernetes where the container process (wildfly in this case) is going to get a TERM signal when the container needs to be moved.

While it's possible to wrapper the process and handle the TERM and then invoke the CLI, it would be preferable for the server process itself to cleanly handle a TERM signal by waiting for in-flight requests to complete (w/ some grace period of course).

Having this as configurable behavior would be good if there are backwards compatibility concerns about introducing this behavior change.