Replace "Unknown board..." message with appropriate exception
Replace "Unknown board..." message with appropriate exception

TimJay/platformio,awong1900/platformio,mplewis/platformio,dkuku/platformio,mcanthony/platformio,awong1900/platformio,platformio/platformio,eiginn/platformio,awong1900/platformio,platformio/platformio-core,bkudria/platformio,TimJay/platformio,TimJay/platformio,bkudria/platformio,jrobeson/platformio,ZachMassia/platformio,jrobeson/platformio,TimJay/platformio,bkudria/platformio,TimJay/platformio,mseroczynski/platformio,atyenoria/platformio,jrobeson/platformio,bkudria/platformio,platformio/platformio-core,jrobeson/platformio,valeros/platformio