CTest: Base command line mode on top of scripting commands

Make sure that all CMake variables that are translated into
CTest options in `cmCTest*Command` implementations are translated
from CTest options into CMake variables before the functions are
called.  This back-and-forth translation should be temporary.
It is a necessary prerequisite for refactoring `cmCTest*Handler`
implementations to operate on CMake variables directly rather
than CTest options.