'Convert opts.prefix_rules to dict.
Convert opts.prefix_rules to dict format. The model for a prefix rule is
(\'<rule name>\',\'<#source_field_lookup>\',\'<pattern>\',\'<prefix>\')
Input:
opts.prefix_rules (tuples): (name, field, pattern, prefix)
Return:
(list): list of prefix_rules dicts'

def get_prefix_rules(self):

    pr = []
    if self.opts.prefix_rules:
        try:
            for rule in self.opts.prefix_rules:
                prefix_rule = {}
                prefix_rule['name'] = rule[0]
                prefix_rule['field'] = rule[1]
                prefix_rule['pattern'] = rule[2]
                prefix_rule['prefix'] = rule[3]
                pr.append(prefix_rule)
        except:
            self.opts.log.error(('malformed    prefix_rules:    %s' % repr(self.opts.prefix_rules)))
            raise
    return pr
