core: Fix broken bll unit test

An error was introduced due to usage of AsyncTaskDao.getAll in the CTOR of the
AsyncTaskManager sinleton

The following patch uses mocking to create mocked data source +
mocked db facade to handle the error.

Change-Id: If70f5da87e1238f0a545496d6e9700151275d642
Signed-off-by: Yair Zaslavsky <yzaslavs@redhat.com>
Signed-off-by: Allon Mureinik <amureini@redhat.com>