Fix false positives from CI build

[per1234]

The previous configuration would only fail if the last compilation of one of the list items failed. Failure of any of the prior compilations in the list item would be masked by a successful final compilation.

For example, compilation of the WiFi_Cloud_Blink example is failing:
https://travis-ci.org/github/arduino-libraries/ArduinoIoTCloud/jobs/663401484#L1782
but the build is passing:
https://travis-ci.org/github/arduino-libraries/ArduinoIoTCloud/builds/663401482

The solution I chose is to use a single buildSketch() function instead of the buildExampleSketch() and buildUtilitySketch() functions. The example sketches to compile are passed as arguments to buildSketch(). The logic for determining the appropriate exit status is built into buildSketch().

[TravisBuddy]

Travis tests have failed

Hey @per1234,
Please read the following log in order to understand the failure reason.
It'll be awesome if you fix what's wrong and commit the changes.

TravisBuddy Request Identifier: 90ebd5f0-6926-11ea-bcbf-610c438bd3d3

[TravisBuddy]

Travis tests have failed

Hey @per1234,
Please read the following log in order to understand the failure reason.
It'll be awesome if you fix what's wrong and commit the changes.

TravisBuddy Request Identifier: edf47250-6928-11ea-bcbf-610c438bd3d3

[aentinger]

Hi @per1234 👋 Thank you very much for reacting so fast on my question with preparing this PR. Do I understand correctly that the CI checks for this PR fail because we already had failing builds inside from before your change? If that's the case I'd still go ahead and merge this in and fix the failing code in a separate PR. What's your opinion?

[per1234]

Do I understand correctly that the CI checks for this PR fail because we already had failing builds inside from before your change?

Correct. The cause of the failed jobs:

/home/travis/build/arduino-libraries/ArduinoIoTCloud/examples/WiFi_Cloud_Blink/WiFi_Cloud_Blink.ino:17:53: error: 'SECRET_WIFI_NAME' was not declared in this scope

 WiFiConnectionHandler ArduinoIoTPreferredConnection(SECRET_WIFI_NAME, SECRET_PASSWORD);

                                                     ^~~~~~~~~~~~~~~~

/home/travis/build/arduino-libraries/ArduinoIoTCloud/examples/WiFi_Cloud_Blink/WiFi_Cloud_Blink.ino:17:71: error: 'SECRET_PASSWORD' was not declared in this scope

 WiFiConnectionHandler ArduinoIoTPreferredConnection(SECRET_WIFI_NAME, SECRET_PASSWORD);

                                                                       ^~~~~~~~~~~~~~~

So the failing CI build actually shows that my change fixes the problem with the false negatives.

I agree that the error in the example sketch should be fixed in a separate PR, since it's not directly related to this one.