Changes

testenv: Log return code of unexpected end of process

This providing further information, for instance if the process actually
exited due to a signal (rc < 0) or due to exiting on its own (rc >= 0).

While at it, rewrite the log line since a process exiting doesn't
necessarily mean it crashed.

Change-Id: I7bbee6ad8e114eeb1ef348184158230b53d0f3cf