test_secrets: Fail in child if sssd_secrets cannot start
    
    If there is a problem to execute sssd_secrets then exception
    is raised. Test will not continue in parent process because it is
    waiting for socket for a second. The child process will continue
    in execution of tests because parent process will kill child
    in teardown after test execution.
    
    This patch makes starting of secret service more robust
    and immediately fail child process when there was a problem to start
    sssd_secrets. It also adds few assertions for ensuring that setup passed
    as it should.
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    (cherry picked from commit f09e045d46ceaa68ba14d79ec0e1a80af8dfbf5f)