tools/dirtometer: Fix failure to write config with non-default isrdir
tools/dirtometer: Fix failure to write config with non-default isrdir

- If isrdir is not set to the default, ~/.isr won't exist and we will
fail to write the config file at shutdown.  We should really be parsing
the client config and determining isrdir, but for now, just create
~/.isr if it doesn't exist.

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr