2261 refactor manual agent logic

[mssalvatore]

What does this PR do?

Fixes #2261

PR Checklist

• Have you added an explanation of what your changes do and why you'd like to include them?
• Is the TravisCI build passing?
• Was the CHANGELOG.md updated to reflect the changes?
• Was the documentation framework updated to reflect the changes?
• Have you checked that you haven't introduced any duplicate code?

Testing Checklist

• Added relevant unit tests?
• Have you successfully tested your changes locally? Elaborate:

  Tested by running unit test
  Tested by running an agent and hitting the stop button

• If applicable, add screenshots or log transcripts of the feature working

[codecov]

Codecov Report

Base: 60.26% // Head: 60.39% // Increases project coverage by +0.12% 🎉

Coverage data is based on head (73841fb) compared to base (4f4eea3).
Patch coverage: 92.85% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2349      +/-   ##
===========================================
+ Coverage    60.26%   60.39%   +0.12%     
===========================================
  Files          539      539              
  Lines        14037    14062      +25     
===========================================
+ Hits          8460     8493      +33     
+ Misses        5577     5569       -8     

Impacted Files	Coverage Δ
monkey/infection_monkey/monkey.py	0.00% <0.00%> (ø)
monkey/monkey_island/cc/models/monkey.py	87.80% <ø> (-1.33%)	⬇️
...onkey_island/cc/repository/i_machine_repository.py	100.00% <ø> (ø)
...y/monkey_island/cc/repository/i_node_repository.py	100.00% <ø> (ø)
monkey/monkey_island/cc/services/database.py	75.00% <ø> (-3.13%)	⬇️
...y/monkey_island/cc/services/infection_lifecycle.py	43.75% <ø> (-20.54%)	⬇️
monkey/monkey_island/cc/services/initialize.py	0.00% <0.00%> (ø)
...ey/monkey_island/cc/setup/island_event_handlers.py	33.33% <33.33%> (ø)
...cc/resources/agent_signals/terminate_all_agents.py	95.65% <95.65%> (ø)
monkey/common/__init__.py	100.00% <100.00%> (ø)
... and 14 more

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