CMR - fixes in the report printing version

Using the raw index like this is fragile, as it has to be changed whenever the columns are changed.  You can use the [`column_index`](https://github.com/dimagi/commcare-hq/blob/0c5ab22927c7ac5499b229c42f675badf2b4231a/custom/opm/reports.py#L761-L765) method for this purpose.  You'll have to move it to the CaseReportMixin first, but then `self.column_index('owner_id')` should just work.