BOARD environment variable check added.
BOARD environment variable check added.

cathalmccabe/PYNQ,Xilinx/PYNQ,cathalmccabe/PYNQ,Xilinx/PYNQ,JorisBolsens/PYNQ,VectorBlox/PYNQ,yunqu/PYNQ,cathalmccabe/PYNQ,yunqu/PYNQ,Xilinx/PYNQ,cathalmccabe/PYNQ,VectorBlox/PYNQ,JorisBolsens/PYNQ,VectorBlox/PYNQ,yunqu/PYNQ,Xilinx/PYNQ,JorisBolsens/PYNQ,yunqu/PYNQ,VectorBlox/PYNQ,JorisBolsens/PYNQ,yunqu/PYNQ,cathalmccabe/PYNQ,schelleg/PYNQ,schelleg/PYNQ,schelleg/PYNQ,schelleg/PYNQ,VectorBlox/PYNQ,JorisBolsens/PYNQ,cathalmccabe/PYNQ,Xilinx/PYNQ,schelleg/PYNQ