Use logname to get the correct user to add to the dialout group

Currently the bm818-tool debian package has hardcoded in it's postinst script the username purism, which will make the package configuration fail, and the package itself not work properly when:

• the end user changed the username in his pureos install
• instalations of mobian, because the default username is mobian and not purism

It also does not account for pmos and nixos, altough those are not debian based.

This patch makes the postint script use logname to determine with what user logged into the device, and adds that user to the dialout group.

Using logname instead of "whoami", echo $USER, "id" to determine what user to add to the dialout group covers the case of the end user installing the package from the root account. Because it would still be the user that logged in that would be added to dialout. Not root.

debian/bm818-tools.postinst

 #!/bin/sh
 
+# check the username used to log in and use that username to be added to dialout
+username=$(logname)
+
 # Add the user to the dialout group for direct ttyUSB3 access
-usermod -a -G dialout purism
+usermod -a -G dialout "$username"