Do not fail migration because of duplicate groups
    
    When 2 groups in a remote LDAP server share the same GID number,
    the migration may fail entirely with incomprehensible message. This
    should not be taken as unrecoverable error - GID number check is
    just a sanity check, a warning is enough. This patch also makes
    sure that GID check warnings include a user name to make
    an investigation easier.
    
    https://fedorahosted.org/freeipa/ticket/2644