Use full relative paths to get module outputs in tests

Make Rel() on ModuleOutPath and ModuleGenPath return the path
relative to the module out and module gen directories respectively,
and make TestingModule.Output() match against the full relative
path to the module.

Test: java_test.go still passes
Change-Id: Id5b2ec3fdef41d4169b943e68d032fc64a2b6f92

android/testing.go

@@ -102,7 +102,7 @@ func (m TestingModule) Output(file string) ModuleBuildParams {
 			outputs = append(outputs, p.Output)
 		}
 		for _, f := range outputs {
-			if f.Base() == file {
+			if f.Rel() == file {
 				return p
 			}
 		}