Turn gtest isolated true by default

Test: presubmit
Bug: 178498003
Change-Id: Ica5584e8b20b5acc92759b384a9263dbd1d4096d
diff --git a/cc/test.go b/cc/test.go
index 5703571..2aadb85 100644
--- a/cc/test.go
+++ b/cc/test.go
@@ -259,7 +259,7 @@
 
 func (test *testDecorator) isolated(ctx BaseModuleContext) bool {
 	if !ctx.Windows() {
-		return BoolDefault(test.LinkerProperties.Isolated, false)
+		return BoolDefault(test.LinkerProperties.Isolated, true)
 	}
 	return BoolDefault(test.LinkerProperties.Isolated, false)
 }