When writing TNG include file closing in wallcycle.

If there is an unwritten frame set when closing a TNG file
it will be written to disk. This includes compressing the
data (when writing compressed output), which can take a
significant amount of time if the system is large.
This should be included in the wallcycle count to make it
more fair.

Change-Id: Ida43fe73b8bc1b0c1326e286a4bff647410da45f