baraction: Simplify update loop
baraction: Simplify update loop

The current loop is a bit awkward for a number of reasons:

  * iostat exits after a number of iterations, so to keep the script
    going we need to run it in a nested loop;

  * we also run iostat concurrently using the |& syntax, which in
    addition to being non-portable requires us to set up a cleanup
    path so that we don't leave stray processes around when spectrwm
    is restarted;

  * due to the fact that iostat prints its headers again every 20
    records, we have to keep careful track of the number of
    iterations - something which has proven to be error-prone.

Once we do away with the idea of iostat driving the update loop, all
of these issues disappear and the code becomes much simpler.

We still cache battery data for 11 seconds, which is the same amount
as before; tweaking it further, if desired, will be trivial now.

This patch is better viewed with 'git show -w'.

conformal/spectrwm,conformal/spectrwm,conformal/spectrwm