set_vmanage_root_cert timeout is too short

[tzarski0]

In many cases when invoking set_vmanage_root_cert, the function will return Exception:
Exception: The request timed out: HTTPSConnectionPool(host='10.62.157.64', port=443): Read timed out. (read timeout=10)
This happens because root CA chain upload might take more than 10s and timeout is hardcoded to 10s. The ask is to raise the default timeout for this function to 20s and allow user to specify custom timeout if root CA chain is very long.