Remove all exit calls

[whaleygeek]

See: https://github.com/Achronite/energenie-ener314rt/issues/8

@Achronite thanks for raising this, added it to my list.

[whaleygeek]

ANALYSIS:

This appears in 2 places in gpio_rpi.c, both in gpio_init()

gpio_rpi.c: 85 exit(-1); //TODO return a result code https://github.com/whaleygeek/pyenergenie/blob/master/src/energenie/drv/gpio_rpi.c#L85

gpio_rpi.c: 104 exit(-1); //TODO return a result code https://github.com/whaleygeek/pyenergenie/blob/master/src/energenie/drv/gpio_rpi.c#L104

The gpio_init() function should be changed to return a GPIO_RESULT that is 0 if ok, and non zero on fail. This can then be checked in the caller (and presumably propagated out in the same way by spi_init() using SPI_RESULT, then radio_init() can return a RADIO_RESULT.

radio.py init() must then check the return result, and raise an exception presumably if it is non zero.

This will then cause init.py init() to throw the exception, then calls to energenie.init() will propagate the exception into the main program. The main programs in all demos should then catch this exception and fail with a message and then hit a finally block, that tries to clean up the GPIO state so it is in a sensible default OFF state (thus allowing another run of the code to succeed if the hardware problem is now fixed);

[Achronite]

My fix can be seen here: https://github.com/Achronite/energenie-ener314rt/blob/master/C/energenie/gpio_rpi.c#L57