F4PGA Flow: restructured tests

[Pocketkid2]

This PR includes (and thus requires) #322

Now tests both VPR and NextPNR flows for F4PGA. VPR uses Yosys the way Symbiflow did, and NextPNR uses Yosys the default way. Also checks for openocd config file. These tests are intended for Xilinx 7 series boards as that is what the new F4PGA module currently supports.