'Combines the given ``lists`` together and returns the result.
The given lists are not altered by this keyword.
Example:
| ${x} = | Combine List | ${L1} | ${L2} |       |
| ${y} = | Combine List | ${L1} | ${L2} | ${L1} |
| ${x} = [\'a\', \'a\', \'b\']
| ${y} = [\'a\', \'a\', \'b\', \'a\']
| ${L1} and ${L2} are not changed.'

def combine_lists(self, *lists):

    ret = []
    for item in lists:
        ret.extend(item)
    return ret
