itest: track and skip flaky tests for windows

To make the CI indicative, we now starting tracking the flaky tests
found when running on Windows. As a starting point, rather than ignore
the windows CI entirely, we now identify there are cases where lnd can
be buggy when running in windows.

We should fix the tests in the future, otherwise the windows build
should be deleted.

itest/lnd_test.go

@@ -238,6 +238,11 @@ func isDarwin() bool {
 	return runtime.GOOS == "darwin"
 }
 
+// isWindowsOS returns true if the test is running on a Windows OS.
+func isWindowsOS() bool {
+	return runtime.GOOS == "windows"
+}
+
 func init() {
 	// Before we start any node, we need to make sure that any btcd node
 	// that is started through the RPC harness uses a unique port as well