Support simplified configuration of the Graceful Shutdown Timeout and Shutdown Timeout in service scripts

The init.d scripts support a SHUTDOWN_WAIT env var that controls how long the stop script will wait for the server process to exit. But there is nothing to control how long graceful shutdown inside the server process should wait, so it defaults to 0.

The existing JBOSS_OPTS env var could be used to set -Dorg.wildfly.sigterm.suspend.timeout=<timeout>, so there already is a way for users to control this. This RFE would be to make this more convenient. That system prop is pretty obscure.

The interaction with SHUTDOWN_WAIT needs be considered. For example a graceful shutdown timeout greater than SHUTDOWN_WAIT is kind of silly, and might be a flaw, as it can lead to forced process termination that otherwise would not occur. Not sure if we want to detect that and do anything. A possibility is to use SHUTDOWN_WAIT to set the graceful timeout (but the process termination wait would need to be a bit longer then, but that doesn't sound good. For one thing it would be a behavior change, where an existing var suddenly has new behavior.