Fix acceptance test for searching just added users in contacts menu

User "user1" is added when installing and configuring the server, so it
is already added in all tests. As the test verifies that just added
users can be searched in the contacts menu a new user should be actually
added.

The test did not fail because it assumed that "user1" did not exist and
just checked that it existed after "adding" it, but not whether adding
it failed.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>