Use @mock.patch.object instead of mock.MagicMock

Some unittests replace methods by mock objects, so they are leave mocked
when unittest finished. It can cause a lot of issues, because when we
try to get access to these attributes in the next test, we get mock
object instead of real attribute. Use @mock.patch.object decorator to
get attributes `unmocked` after test.

Change-Id: I23b3926a7671e0669315836da787ec88a812d67b
Merge "Use @mock.patch.object instead of mock.MagicMock"