Implement membership change integration tests

[jopemachine]

Let's break down the approach to the membership change test in a more detailed manner.
Specifically, we will need integration test cases for the following scenarios because a different handler is executed in each case.

• Membership change request for a single ConfChange of AddNode.
• Membership change request for a single ConfChange of RemoveNode.
• Membership change request for multiple ConfChange of AddNode.
• Membership change request for multiple ConfChange of RemoveNode.
• Membership change request for mixed ConfChange of AddNode and RemoveNode.
  • In this case, resolving issue Support mixed AddNode and RemoveNode for ConfChangeV2 request #172 must take precedence.