veyron/services/mgmt/build: respecting the GOROOT environment variable
setting in order to make the build server test pass with Go 1.4

Change-Id: If6b8430b1cf491b4fc4d2e3d9ef1cfdbb3ce4877
diff --git a/services/mgmt/build/impl/impl_test.go b/services/mgmt/build/impl/impl_test.go
index 4dfc78a..85b4773 100644
--- a/services/mgmt/build/impl/impl_test.go
+++ b/services/mgmt/build/impl/impl_test.go
@@ -48,7 +48,7 @@
 			t.Fatalf("LookPath(%q) failed: %v", name, err)
 		}
 	}
-	return pathbin, ""
+	return pathbin, os.Getenv("GOROOT")
 }
 
 // startServer starts the build server.