Helper methods for plugin and notification setup were previously
defined on neutron.tests.base.BaseTestCase. The imports required to
support these helpers were preventing the api tests from consuming
tempest due to configuration conflicts that resulted between neutron
and tempest. This change moves the helpers to a new module in
tests/unit so that BaseTestCase can be safely used across all types of
tests.
Partially-Implements: blueprint retargetable-functional-testing
Change-Id: I44251db399cd73390a9d1931a7f253662002ba10
5558a3c1b9