[vcf_etl%vcf_record] Change `i` by `x` or `item`.

[segarmond]

For code chunk:

        if type(value) == list:
            test_call = []
            for i in value:
                test_call.append(type(i)==RecordCall)
            if all(test_call):
                self._calls = value

Change i by x or item since i could be confused as an iterator.