Replace android.BuildOs with Config.BuildOS

Replace the android.BuildOs constant with Config.BuildOS so that it
can vary based on the product config.

Bug: 190084016
Test: all Soong tests
Change-Id: Ia67f872d8b2ab788747a22e3a9659dc21c9775cd
diff --git a/java/plugin_test.go b/java/plugin_test.go
index c7913d3..dc29b1c 100644
--- a/java/plugin_test.go
+++ b/java/plugin_test.go
@@ -15,7 +15,6 @@
 package java
 
 import (
-	"android/soong/android"
 	"testing"
 )
 
@@ -58,7 +57,7 @@
 		}
 	`)
 
-	buildOS := android.BuildOs.String()
+	buildOS := ctx.Config().BuildOS.String()
 
 	javac := ctx.ModuleForTests("foo", "android_common").Rule("javac")
 	turbine := ctx.ModuleForTests("foo", "android_common").MaybeRule("turbine")
@@ -98,7 +97,7 @@
 		}
 	`)
 
-	buildOS := android.BuildOs.String()
+	buildOS := ctx.Config().BuildOS.String()
 
 	javac := ctx.ModuleForTests("foo", "android_common").Rule("javac")
 	turbine := ctx.ModuleForTests("foo", "android_common").MaybeRule("turbine")