adding first unit test for search of address book provider


refs https://github.com/owncloud/contacts/pull/545#issuecomment-51184645
I think you shouldn't manually create a test contact here when the Max Mustermann contact is already provided by mock.php, and filled with attributes like FN and UID from test1.vcf. Just use `Backend\Mock('foobar')` instead of `Backend\Database($user)`. Take a look at `contact_test.php` to see how it's done there.