Fix #687: verbosity is not a flag

The issue is that `nosetests.cfgToArg()` was treating the verbosity flag
as a boolean when you set the value to `1` in `setup.cfg`.  Instead of
using the `flag()` helper, let's consult the option object and see if
the action is `store_true` or `store_false`.
Merge pull request #688 from jszakmeister/fix-issue-687

Fix #687: verbosity is not a flag