Make sdk tests more realistic

The tests use <sdk>_<module>_<version> as the format for a versioned
sdk member name but the format should be <sdk>_<module>@<version>. This
change corrects it and also fixes a similar issue in an error message.

Bug: 181569894
Test: m nothing
Change-Id: I8be0db4bcd0b6f4d6fbdf9e402ef7257fae8e18b
diff --git a/android/sdk.go b/android/sdk.go
index 6fc1910..8992bab 100644
--- a/android/sdk.go
+++ b/android/sdk.go
@@ -82,7 +82,7 @@
 func ParseSdkRef(ctx BaseModuleContext, str string, property string) SdkRef {
 	tokens := strings.Split(str, string(SdkVersionSeparator))
 	if len(tokens) < 1 || len(tokens) > 2 {
-		ctx.PropertyErrorf(property, "%q does not follow name#version syntax", str)
+		ctx.PropertyErrorf(property, "%q does not follow name@version syntax", str)
 		return SdkRef{Name: "invalid sdk name", Version: "invalid sdk version"}
 	}