Change writeln()s of format()ed strings to writef()s

This was written before we had writef() in the library, so it
used a number of format() conversions which are pretty ugly
and heavyweight.  Changing to writef() for simplicity and
clarity.
Merge pull request #708 from bradcray/lulesh-regressions-week

Change writeln()s of format()ed strings to writef()s in LULESH

[trivial, not reviewed]

Lulesh was written before we had writef() in the library, so it
used a number of format() conversions which are pretty ugly
and heavyweight. Changing to writef() for simplicity and
clarity.

I was having trouble debugging an issue in LULESH which
motivated this change.