do not run remote tests if AUTH_SERVER is unset

pam/auth_client_test.cc

@@ -126,7 +126,8 @@ TEST_F(AuthClientTest, SSLFailsWithBadCAServerSide) {
 int main(int argc, char **argv) {
   server = getenv("AUTH_SERVER");
   if (server == NULL) {
-    server = "localhost:1617";
+    printf("This test requires a local auth server. Set the AUTH_SERVER environment variable to its address.\n");
+    exit(0);
   }
 
   ::testing::InitGoogleTest(&argc, argv);