Add tests for cluster commands.
Add tests for cluster commands.

Still need to add tests for cluster update and cluster create subcommands.
Right now, I am capturing calls to Connection._api_call().
It is probably a better idea to capture calls to the requests library itself.
That's in the to-do list.

yogesh2021/qds-sdk-py,rohitpruthi95/qds-sdk-py,tanishgupta1/qds-sdk-py-1,jainavi/qds-sdk-py,msumit/qds-sdk-py,qubole/qds-sdk-py,vrajat/qds-sdk-py,prakharjain09/qds-sdk-py,adeshr/qds-sdk-py