Add universal build_type variant to CMakePackage (#4797)

* Add universal build_type variant to CMakePackage
* Override build_type in some packages with different possible values
* Remove reference to no longer existent debug variant
* Update CBTF packages with new build_type variant
* Keep note on build size of LLVM

var/spack/repos/builtin/packages/cbtf-krell/package.py

@@ -68,6 +68,8 @@ class CbtfKrell(CMakePackage):
             description="Build mpi experiment collector for mpich2 MPI.")
     variant('mpich', default=False,
             description="Build mpi experiment collector for mpich MPI.")
+    variant('build_type', default='None', values=('None'),
+            description='CMake build type')
 
     # Dependencies for cbtf-krell
     depends_on("cmake@3.0.2:", type='build')
@@ -129,9 +131,6 @@ def set_mpi_cmakeOptions(self, spec, cmakeOptions):
 
         cmakeOptions.extend(MPIOptions)
 
-    def build_type(self):
-        return 'None'
-
     def cmake_args(self):
         spec = self.spec