Rename 'old_parser' configuration to 'force_llvm'

It does use the old parser, but it also forces the use
of the llvm tier for everything which usually ends up being
the more important part of the configuration.

CMakeLists.txt

@@ -287,7 +287,7 @@ endmacro()
 
 # tests         testname directory arguments
 add_pyston_test(defaults tests --order-by-mtime)
-add_pyston_test(old_parser tests -a=-n -a=-x -t50)
+add_pyston_test(force_llvm tests -a=-n -a=-x -t50)
 if(${CMAKE_BUILD_TYPE} STREQUAL "Release")
   add_pyston_test(max_compilation_tier tests -a=-O -a=-x -t50)
 endif()