[Kubernetes] Add ability to Setup HA Kubernetes Master for Virtual Switch Testbed

[isabelmsft]

Description of PR

Summary:

This PR introduces the ability to setup a HA Kubernetes master on the same internal management network as used by the virtual switch testbed.

Type of change

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

Approach

What is the motivation for this PR?

We need this to test Kubernetes features on the virtual switch testbed.

How did you do it?

1. Added script to set up NAT for br1 internal management network, so Kubernetes master Ubuntu KVMs can reach internet
2. Defined new ansible inventory file for Kubernetes VMs on internal management network
3. Added DNS server IP configuration to Ubuntu KVms
4. Updated k8s testbed README to describe steps to set up HA Master for virtual switch testbed
   Unrelated to this PR, I also adjusted a few permissions to fix an issue when setting up HA master by user with different permissions

How did you verify/test it?

• Created HA Kubernetes master on internal k8s management network, using testbed-cli.sh script
• Joined virtual switch to Kubernetes master on internal management network
• Passed k8s/test_join_available_master.py on virtual switch vlab-01

isl@5222e4a8cc5a:/data/sonic-mgmt/tests$ ./run_tests.sh -d vlab-01 -n vms-kvm-t0 -f ../ansible/vtestbed.csv -i ../ansible/veos_vtb,../ansible/k8s_ubuntu_vtb -u -b 21_1 -c k8s/test_join_available_master.py 
=== Running tests in groups ===
/usr/local/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py:44: CryptographyDeprecationWarning: Python 2 is no longer supported by the Python core team. Support for it is now deprecated in cryptography, and will be removed in a future release.
  from cryptography.exceptions import InvalidSignature
========================================================================================= test session starts ==========================================================================================
platform linux2 -- Python 2.7.17, pytest-4.6.5, py-1.9.0, pluggy-0.13.1
ansible: 2.8.12
rootdir: /data/sonic-mgmt/tests, inifile: pytest.ini
plugins: html-1.22.1, forked-1.3.0, xdist-1.28.0, metadata-1.10.0, repeat-0.8.0, ansible-2.2.2
collected 1 item                                                                                                                                                                                       

k8s/test_join_available_master.py::test_join_available_master PASSED                                                                                                                             [100%]

------------------------------------------------------------------------ generated xml file: /data/sonic-mgmt/tests/logs/tr.xml ------------------------------------------------------------------------
====================================================================================== 1 passed in 328.99 seconds ======================================================================================

[lguohan]

ansible/.k8s_ubuntu_vtb.swp, let's remove it.

[lguohan]

lgtm, please resolve the conflict.