ASV: occasional asv failures on xlwt
https://travis-ci.org/pandas-dev/pandas-ci/jobs/343616367
this is on current pandas master (this is just the CI job running it).

excel asv's

```
The following asvs benchmarks (if any) failed.
[ 43.02%] ··· Running io.excel.Excel.time_read_excel                  1/3 failed
                   xlwt      failed 
DONE displaying failed asvs benchmarks.
```

I have seen this work as well. maybe a race-condition?