Give rpi_hardware_version a clearly invalid value by default.
Give rpi_hardware_version a clearly invalid value by default.

yodaaut/raspbian-ua-netinst,racing-tech/rrp-raspi-installer,firepick/FireHawk,Zeerix/raspbian-ua-netinst,beylsp/rpi-installer,beylsp/rpi-installer,kolargol/raspbian-ua-netinst,cybercircuits/raspbian-ua-netinst,dicer/raspbian-ua-netinst,jturner314/raspbian-ua-netinst,matt2005/raspbian-ua-netinst,malsony/raspbian-ua-netinst,daytonpid/FireHawk,racing-tech/rrp-raspi-installer,FooDeas/raspberrypi-ua-netinst