Fix #30: use the last line as current result

fix #30

Author: Davies Liu <davies.liu@gmail.com>

Closes #32 from davies/fix_30 and squashes the following commits:

12d3281 [Davies Liu] Merge branch 'master' of github.com:databricks/spark-perf into fix_30
d2a409c [Davies Liu] fix for spark-test and mllib tests
6f36ebb [Davies Liu] fix #30, fetch the latest results from output