Make Pytest framework thin wrapper around client_cli

[appetrosyan]

I don't think we need yet another level of abstraction over client_cli:

1. no need to learn yet another framework to write a test
2. makes you more familiar with iroha_client_cli API
3. nothing is obfuscated away
4. we should be focusing on implementing missing functionality in iroha_client_cli

All we need is a way to parse output, we don't need a way to construct the input

_Originally posted by @mversic in
#3490