ipatests: change logdir naming pattern for multihost tests
    
    Remove brackets from the paths in naming pattern of directories
    for multihost logs. Brackets in filenames require special handling
    in markdown URLs, bash paths etc.
    
    Related: https://pagure.io/freeipa/issue/6971
    
    Signed-off-by: Tomas Krizek <tkrizek@redhat.com>
    Reviewed-By: Martin Basti <mbasti@redhat.com>