Refactor to rename mock package to be mocks

[irainia]

If we check the current implementation, we have mock package to store any mock structure for testing purposes. Instead of using mock, I suggest to change it into mocks instead. The following is the pros in doing so:

• if we use mockery, the minimum default behavior of it is to generate package mocks instead of mock
  • why using this tool? it is just to simplify in creating the mock structure
• since we are using testify, at some points we use its mock package, which causes package import conflict with our own mock package. our solution right now is by using alias like mock2. we can reduce this alias by using this mocks package instead.