Fix the platform_info test failure because of callback loader

[sujinmkang]

Description of PR

platform_info test on 201811 branch failed with following error

test_show_platform_summary
ImportError while loading conftest '/var/sonicbld/workspace/NewTests/platform_info/tests/conftest.py'.
conftest.py:9: in <module>
    from ansible_host import AnsibleHost
ansible_host.py:1: in <module>
    from ansible.plugins import callback_loader
E   ImportError: cannot import name callback_loader

Summary:
Fixes # (issue)
change to pick up the proper path for the callback_loader plugin path based on ansible version

Type of change

• [x ] Bug fix
• Testbed and Framework(new/improvement)
• Test case(new/improvement)

Approach

How did you do it?

Import the callback_loader from the right path

How did you verify/test it?

Run test_platform_info.py

Any platform specific information?

N/A

Supported testbed topology if it's a new test case?

N/A

Documentation

[qiluo-msft]

Do you want to PR against master, and cherry-pick to 201811?

[lguohan]

agree with @qiluo-msft

[sujinmkang]

@qiluo-msft and @lguohan Since master branch supports the latest version of ansible from beginning and it only import the callback_loader from the new ansible path, I thought it will be ok to keep the change in master as is but for 201811, the ansible version changed later so I added this change to support both old and new ansible plugin version.
To make the code consistent for master and 201811, I can create a new PR against master and cherry-pick to 201811.

[sujinmkang]

@qiluo-msft and @lguohan ansible_host.py is removed on master with (#1658) so it's not possible to pr to master.