Reworking of lapack_shared_libs and similar properties (#1682)

* Turned <provider>_libs into an iterable

Modifications :
- added class LibraryList + unit tests
- added convenience functions `find_libraries` and `dedupe`
- modifed non Intel blas/lapack providers
- modified packages using blas_shared_libs and similar functions

* atlas : added pthread variant

* intel packages : added lapack_libs and blas_libs

* find_library_path : removed unused function

* PR review : fixed last issues

* LibraryList : added test on __add__ return type

* LibraryList : added __radd__ fixed unit tests

fix : failing unit tests due to missing `self`

* cp2k and dependecies : fixed blas-lapack related statements in package.py

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

@@ -42,7 +42,7 @@ def install(self, spec, prefix):
             '-DCMAKE_POSITION_INDEPENDENT_CODE=ON',
             # BLAS support
             '-Denable_blaslib=OFF',
-            '-DBLAS_blas_LIBRARY={0}'.format(spec['blas'].blas_shared_lib)
+            '-DBLAS_blas_LIBRARY={0}'.format(spec['blas'].blas_libs.joined())
         ]
 
         cmake_args.extend(std_cmake_args)