ValueError: could not convert string to float when running test_column_sum_min_max

I am seeing this error when running `s3tests_boto3`

```
======================================================================
ERROR: s3tests_boto3.functional.test_s3select.test_column_sum_min_max
----------------------------------------------------------------------
Traceback (most recent call last):
File "/root/s3-tests/virtualenv/lib/python3.6/site-packages/nose/case.py", line 198, in runTest
self.test(*self.arg)
File "/root/s3-tests/s3tests_boto3/functional/test_s3select.py", line 233, in test_column_sum_min_max
nose.tools.assert_equal( float(res_s3select), float(res_target))
ValueError: could not convert string to float: '\navg function not found\n'
```

I am executing the tests from `ceph_pacific` branch.