Add SANLOCK_PRIVILEGED environment variable
    
    Setting this variable to 0, sanlock daemon will skip operations that
    requires privileges. This allows running sanlock daemon as regular user
    in the tests.
    
    When running the daemon, we log a warning if this variable is set to to
    non default value.
    
    Signed-off-by: Nir Soffer <nsoffer@redhat.com>