mqtt: container should check for agent id in mirrored container

[maurerle]

The mqtt container should check if the receiver ID exists in the mirrored container pass the message to it.

This also cleans up as_agent_process in tcp container, which is now handled in the core and only differs through _create_mirror_container.

Would like to merge this before #166

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.15%. Comparing base (d3adc04) to head (76c70ad).
Report is 2 commits behind head on development.

Additional details and impacted files

@@               Coverage Diff               @@
##           development     #167      +/-   ##
===============================================
+ Coverage        89.13%   89.15%   +0.01%     
===============================================
  Files               22       22              
  Lines             2513     2507       -6     
===============================================
- Hits              2240     2235       -5     
+ Misses             273      272       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.