fetch2: gitsm: fix incorrect handling of git submodule relative urls
    
    As specified by git submodule manual relative urls can start either
    with '..' or './', second case was incorrectly managed leading to an
    interpretation of urls starting with './' as absoulte urls.
    
    Signed-off-by: Gennaro Iorio <gennaro.iorio@schindler.com>
    Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>