Refactor OpenADRVENAgent

[bonicim]

Description

• Upgrades openleadr library to latest to ensure that cryptography does not get downgraded in Volttron. See related PR at Fix cryptography version constraint OpenLEADR/openleadr-python#129
  * NOTE: the requirement for openleadr 0.5.27 will force the Volttron platform to upgrade from cryptography 37.0.4 to 38.0.4 By explicitly adding Volttron's cryptography requirement to OpenADRVEN's requirements.py, we prevent the library openleadr from upgrading or downgrading requirements.py whenever the agent is installed.
• Refactors OpenADRAgent to use Adapter pattern to create a separation between the VolttronOpenADRVenClient and the OpenLeadr client
• Fixes bug in config parsing method
• Updates test
• Reformats code to PEP8 compliance

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

I manually created an agent against the IPKeys test VTN.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

[bonicim]

bump @shwethanidd @craig8 I have pinned cryptography in this agent's requirements.txt to match Volttron's. When I installed the agent using vctl I saw that the version of cryptography remained at Volttron's version, which is the intent.