MINIFICPP-1596 Refactor docker tests by removing unnecessary clusters

[lordgamez]

Issues addressed in this PR regarding integration tests:

• The main problem was the misuse of the Cluster concept in the codebase causing several issues
• Cluster and Container concepts were mixed up in the codebase which made understanding the test code harder
• In several test scenarios multiple clusters were created with the same network, which made the cleanup cumbersome and fail transiently
• Some container deployments required creating new named clusters that were unnecessary and made the test scenario descriptions more complex
• The SingleNodeDockerCluster class had way too many responsibilities handling attributes corresponding to specific containers
• There were some redundancies in the test step definitions
• Custom images are built separately for every test case

Changes made to resolve the issues:

• The SingleNodeDockerCluster (single node referring to the intent of running the containers on a single compute node) is now defined as a set of Containers with a single Docker network connecting them
• All test scenarios now have a single cluster which makes the cleanup much simpler and no multiple named clusters in the test steps are needed
• Introducing the container concept in the code with the Container class from which all used containers are inherited from defining their own attributes, deployment functions and so on. This moves container specific functionality from the SingleNodeDockerCluster and simplifies the deployment of the cluster
• Removing the redundancies from the step descriptions which simplifies the test scenarios
• Adding ImageStore to cache built custom images and reuse them in additional testcases, additionally NiFi and MiNiFi configuration files are attached as volumes instead of building them in the image
• Fixing some timing issues to lower runtimes

Jira ticket: https://issues.apache.org/jira/browse/MINIFICPP-1596
This should also fix the following Jira regarding transient failures in cleanup: https://issues.apache.org/jira/browse/MINIFICPP-1516

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