Get pubsub numsub working

PUBSUB NUMSUB did not work

Expected Results

Command returns number of subscribers to list of channels.

Actual Results

Error. Two problems -

1. command needs to be in two parts - command and sub command.
2. the results need to be parsed in pairs - channel and count.

Steps to Reproduce

1. Run the test I've just written.

Checklist:

• Copyright headers in new files (see CONTRIBUTING.md)
• Unit test case to prevent the bug in the future