allow for running tests without networking

[06kellyjac]

I'd like the tests that require networking to be optional/toggle-able off for running within the nix sandbox which doesn't allow network access Currently I just rm pkg/scanner/scan_test.go https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/tools/dockle/default.nix#L25

This can be achieved with go flags

https://blog.jbowen.dev/2019/08/using-go-flags-in-tests/

https://stackoverflow.com/questions/25965584/separating-unit-tests-and-integration-tests-in-go