compiletest: Run all android tests serially

This is an attempt to isolate test failures on the bots. It may also
eliminate problems with the emulators breaking by reducing the chance
of OOM.

src/compiletest/compiletest.rs

@@ -219,12 +219,14 @@ pub fn run_tests(config: &config) {
             mode_debug_info => {
                 println!("arm-linux-androideabi debug-info \
                          test uses tcp 5039 port. please reserve it");
-                //arm-linux-androideabi debug-info test uses remote debugger
-                //so, we test 1 task at once
-                os::setenv("RUST_TEST_TASKS","1");
             }
             _ =>{}
         }
+
+        //arm-linux-androideabi debug-info test uses remote debugger
+        //so, we test 1 task at once.
+        // also trying to isolate problems with adb_run_wrapper.sh ilooping
+        os::setenv("RUST_TEST_TASKS","1");
     }
 
     let opts = test_opts(config);