Refactor HostCollectionTest class
Refactor HostCollectionTest class

This commit introduces the following changes:
* adding BaseHostCollectionTest class and making it
the parent class of HostCollectionTest.
* moving the original code from HostColletionTest to BaseHostCollectionTest
* introduction of constructor class property to HostCollectionTest and
BaseHostCollection, and using it in BaseHostCollection instead of constructor
of HostCollection class
* making test methods for BaseHostCollection.add method use
BaseHostCollectionTest._set_matching_hosts

piotr-rusin/spam-lists