Allow default setting of ARDUINO_DIR for Cosa build script.
Allow default setting of ARDUINO_DIR for Cosa build script.

kc9jud/Cosa,rrobinet/Cosa,jeditekunum/Cosa,dansut/Cosa,jeditekunum/Cosa,rrobinet/Cosa,mikaelpatel/Cosa,dansut/Cosa,jeditekunum/Cosa,mikaelpatel/Cosa,kc9jud/Cosa,jeditekunum/Cosa,mikaelpatel/Cosa,rrobinet/Cosa,rrobinet/Cosa,kc9jud/Cosa,kc9jud/Cosa,dansut/Cosa,dansut/Cosa,mikaelpatel/Cosa