[Cmake] Fixed wrong set() syntax in cmake files

- Files CTestConfig.cmake and Options.cmake were affected

- The variable BUILDNAME is declared to be INTERNAL; this
  means that it should not be displayed in any GUI. However,
  as the "keyword" (note the quotation marks here) TYPE was
  given (this does not exist!), it was still displayed; however,
  the "docstring" property was missing, so I added it.

- Check out the documentation here:
  http://www.cmake.org/cmake/help/v2.8.7/cmake.html#section_Properties