Small but important tweaks to fix the operation of the nut initscripts
and hotplug scripts.  All hail shellcheck and proofreading and
dogfooding.

Signed-off-by: Daniel F. Dickinson <cshored@thecshore.com>

When using serial-port based UPSes with NUT, it is handy to be able to
configure a USB serial port to have be set tot the NUT runas user, so
that NUT can access the serial port automagically.
Closes #6997

Signed-off-by: Daniel F. Dickinson <cshored@thecshore.com>