Don't use real Jira API responses in tests

[aik099]

Currently, we mock Jira API communication in tests and provide working Jira API responses back. In most cases, this doesn't make sense to do, because we're just returning the json-decoded version of whatever Jira API returns.

Unless after an API call is made we're parsing the response and doing something extra (e.g. Api::getPriorities), then using real Jira API response in the test suite makes no sense.