Improved handling of OTA initialisation

[cdjackson]

@hanneshofmann this ought to resolve the issue with the OTA initialisation. I've not tested it as it will fail compilation at the moment until the libraries are updated.
Closes #312
Signed-off-by: Chris Jackson [email protected]

[hanneshofmann]

Thanks for the improvement - the code looks good to me and my local tests were successful (using this PR and zsmartsystems/com.zsmartsystems.zigbee#443) . I think we could merge it as soon as the libraries are updated.

As already pointed out in #312, there are still some problems to fully update the device firmware due to some transactions timeouts. Since these timeouts seem unrelated to the OTA initialization, I will collect some logs and I will create a new issue for that.

[cdjackson]

Thanks. The timeouts may be device issues (some devices don't respond to the final message in the transfer), but as mentioned, raise an issue and provide the logs and I'll take a look.

[cdjackson]

Requires #332

[cdjackson]

Merging as already reviewed above by @hanneshofmann