SIGTERM on shell task with monitor is forwarded to shell process, in Universal Agent

Same as JS-1307, but for Universal Agent.

A task process, running a monitored shell process, receiving a SIGTERM signal catches the signal and forwards it to the shell process. After that, the task process is expected to terminate.

With this change, a SIGTERM acts directly on the monitored shell process. The monitor has the chance to execute the post-processing methods.