Change container's exec_run function to return tuple of (function that returns exit_code, output) when stream/socket=True

[tzah4748]

Inspired by: #2557

As explained in issue above, getting the exit code might be needed even when running with socket or stream set to True.
This can be easily achieved by returning a function that returns that exit code.

A simple use case:

async def _log_exec_result(exec_result: ExecResult):
    generator: Iterable = exec_result.output
    while exec_result.exit_code() is None:
        # Program still running
        output = next(generator, None)  # Assuming the generator has no None values
        if output is not None:
            # print/log
        else:
            # some sleep or w/e

exec_result = my_container.exec_run('/run/server/that/shows/requests/output', stream=True)
_log_exec_result(exec_result)
# Freely continue the program while logging the server outputs.

Note the above assumes (this behaviour was tested) that the exit code returned is None until the executed command/program finishes.

Signed-off-by: Tzah Mazuz tmazuz@nvidia.com