Retry sketch verification after arduino exit status 3

[per1234]

I've been encountering some build failures when compiling for ESP8266 that return exit status 3 with an "unknown package" error message. These are sporadic and other sketch compilations for ESP8266 in the same job will not have the problem. The job completes successfully after being restarted.

I suspect this is caused by temporary unavailability of the ESP8266 Boards Manager JSON file.

A possible workaround is to automatically retry the verification after arduino exit status 3, as I already do for undocumented exit codes (https://github.com/per1234/arduino-ci-script/blob/1.0.0/arduino-ci-script.sh#L785).