config_helper.py doesn't handle negative int correctly

The check-in is supposed to fix bug 1235702.

But handling float parameters takes much more tests,
thus we leave this part for later.

Partially Close-bug: #1235702
Change-Id: I08ca62c577ddda5083e08391b0693455d6ca68dc
Merge "config_helper.py doesn't handle negative int correctly"