More information on storage failure

[SeaTechRC]

Hello,

As of now there is no exact explanation for when the storage module failed to write to flash.
In order to be able to differentiate between different failure modes, the error message includes the esp_err_t string in the sotrage class.

[falkoschindler]

Thanks for the pull request, @SeaTechRC!

The inline assignment if ((err = ...) != ESP_OK) { is a bit unconventional, but fine with me.

Assuming you already compiled and tested the implementation, I happily approve the PR. 👍🏻

[falkoschindler]

I compiled it myself and noticed an error due to declaring err but using error. This was easy to fix.
But now I feel like testing it on a real ESP at least once before merging.

[falkoschindler]

Ok, I erased the storage of an ESP using esptool.py erase_flash and - after flashing and restarting - got the expected error message including the error name "ESP_ERR_NVS_NOT_FOUND":

error while loading startup script: could not peek storage storage.num_chunks (ESP_ERR_NVS_NOT_FOUND)