Use absolute paths in classpaths.proto.

The intention before was to use relative paths to a partition where a
config is defined. However, jars in /system_ext partition are planned to
be declared in /system's classpaths.proto config.

Bug: 180105615
Test: derive_classpath_test, CtsClasspathsTestCases
Change-Id: Icc3e1a903c34187cfcd67a3ae7bc3dd746445c03
Merged-In: Icc3e1a903c34187cfcd67a3ae7bc3dd746445c03
(cherry picked from commit 7d22657c458b7cf7f79cdd3c298bfec13be93533)

java/classpath_fragment.go

@@ -136,7 +136,7 @@ func writeClasspathsJson(ctx android.ModuleContext, output android.WritablePath,
 	for idx, jar := range jars {
 		fmt.Fprintf(&content, "{\n")
 
-		fmt.Fprintf(&content, "\"relativePath\": \"%s\",\n", jar.path)
+		fmt.Fprintf(&content, "\"path\": \"%s\",\n", jar.path)
 		fmt.Fprintf(&content, "\"classpath\": \"%s\"\n", jar.classpath)
 
 		if idx < len(jars)-1 {