[reboot test] call sudo reboot to reboot dut (#452)

* [reboot test] call sudo reboot to reboot dut

- Using reboot allow the dut to reboot with platform specific reboot tools.
- Ansible behaves differently with "become: yes + reboot" and "sudo reboot"
  It appears that only the later could reboot the DUT.
  This behavior might have caused by sonic intercepts reboot with a script.

* [reboot test] improvoe test description

* [reboot test] improve test message, take 2

Author: yxieca

ansible/roles/test/tasks/common_tasks/reboot_sonic.yml

@@ -1,6 +1,5 @@
-- name: reboot
-  become: true
-  shell: shutdown -r now "Warning! System is being rebooted remotely by reboot_sonic.yml"
+- name: "rebooting {{ inventory_hostname }} : {{ ansible_host }} ..."
+  shell: sudo reboot
   async: 1
   poll: 0
   ignore_errors: true