Very ugly way to convert the granule identifier.

    e.g.
    From
    Granule Identifier:
    S2A_OPER_MSI_L1C_TL_SGS__20150817T131818_A000792_T28QBG_N01.03
    To
    Granule Metadata XML name:
    S2A_OPER_MTD_L1C_TL_SGS__20150817T131818_A000792_T28QBG.xml

def _granule_identifier_to_xml_name(granule_identifier):
    """
    Very ugly way to convert the granule identifier.

    e.g.
    From
    Granule Identifier:
    S2A_OPER_MSI_L1C_TL_SGS__20150817T131818_A000792_T28QBG_N01.03
    To
    Granule Metadata XML name:
    S2A_OPER_MTD_L1C_TL_SGS__20150817T131818_A000792_T28QBG.xml
    """
    # Replace "MSI" with "MTD".
    changed_item_type = re.sub("_MSI_", "_MTD_", granule_identifier)
    # Split string up by underscores.
    split_by_underscores = changed_item_type.split("_")
    del split_by_underscores[-1]
    cleaned = str()
    # Stitch string list together, adding the previously removed underscores.
    for i in split_by_underscores:
        cleaned += (i + "_")
    # Remove last underscore and append XML file extension.
    out_xml = cleaned[:-1] + ".xml"

    return out_xml