Fix CMake notation for VerifyFields tests

Fix the variable reference notation used in setting the LOGFILENAME for
the VerifyFields tests.  Remove the "@@" notation and replace it with the
"${}".  This will eliminate configure warning when using a more recent
version of CMake.

OSEHRA-Id: http://issues.osehra.org/browse/OAT-155
Change-Id: Iae831a3dc11d20b964229e0aeb3478789f3ae9fd