pmbootstrap: kill process if no output was written for 5 minutes

Created by: ollieparanoid

I'm currently implementing a --timeout flag (defaults to 5 minutes), which causes non-interactive subprocesses to be killed if they don't write any output in that time. Motivation for that are the build problems in the binary repository - some packages (qt5-qtwebengine and at least two kde packages) may sometimes stop the build at some point and need to be restarted. That isn't necessarily their fault, it may be caused by our build setup that involves QEMU for everything except for the compiler when cross compiling. You can imagine how annoying that is when trying to build packages for the binary repository while being AFK for multiple hours. With the automatic killing in place, the repository script would simply retry after failure.

Of course doing it that way is not the real fix, but it is a good short term solution and a nice safety feature in general if builds stop in the future for whatever reason. I want to find the root cause of the issue as well, but that will take me more time.