LBANN flags and OpenCV variant (#5951)

* Fixed the datatype flag in the LBANN package.
Fixed where the datatype flag should be set.

* Added variant to OpenCV to disable building DNN support

* Fixed a bug in how the elemental package tries to find its Fortran
library.  The current method does not work with Intel compilers.

* Added necessary paths for cuDNN and CUB.

* Addressed flake8 issues in Elemental package.

* Fixed several flake8 errors.  Added variant to build with or without
support for arbitrary-precision floating point arithmetic.

* Added the proper CMake flag when MPFR support is disabled.

* Fixed a bug in how the cudnn path was being set when there was no
cudnn requested.  Also requested that OpenCV is built without eigen
support.

* Fixed another bug where a dependency may not be there and thus should
not be always checked.

var/spack/repos/builtin/packages/lbann/package.py

@@ -48,9 +48,11 @@ class Lbann(CMakePackage):
     depends_on('elemental +openmp_blas +shared +int64 build_type=Debug', 
                when=('build_type=Debug'))
     depends_on('cuda', when='+gpu')
+    depends_on('cudnn', when='+gpu')
+    depends_on('cub', when='+gpu')
     depends_on('mpi')
     depends_on('hwloc')
-    depends_on('opencv@3.2.0: +openmp +core +highgui +imgproc +jpeg +png +tiff +zlib', when='+opencv')
+    depends_on('opencv@3.2.0: +openmp +core +highgui +imgproc +jpeg +png +tiff +zlib ~eigen', when='+opencv')
     depends_on('protobuf@3.0.2:')
     depends_on('cnpy')
 
@@ -83,4 +85,12 @@ def cmake_args(self):
             args.extend(['-DOpenCV_DIR:STRING={0}'.format(
                 spec['opencv'].prefix)])
 
+        if '+cudnn' in spec:
+            args.extend(['-DcuDNN_DIR={0}'.format(
+                spec['cudnn'].prefix)])
+
+        if '+cudnn' in spec:
+            args.extend(['-DCUB_DIR={0}'.format(
+                spec['cub'].prefix)])
+
         return args