Add method to validate Internet connectivity

[kdart]

Could use a generic method to open a socket to an external site that can used instead of curl. This should be easy enough and will eliminate the need for curl on the device.

[xpconanfan]

This might be more difficult than it is.
Internet connectivity means different things for different use cases.
And the network APIs have been changing from version to version.

I think there's a NetworkDiagnostics class added in M for this purpose
Feel free to give this a try :)

[kdart]

Added in recent PR.