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/wannier90/package.py

@@ -47,13 +47,12 @@ class Wannier90(Package):
 
     def install(self, spec, prefix):
 
+        lapack = self.spec['lapack'].lapack_libs
+        blas = self.spec['blas'].blas_libs
         substitutions = {
             '@F90': spack_fc,
             '@MPIF90': self.spec['mpi'].mpifc,
-            '@LIBS': ' '.join([
-                self.spec['lapack'].lapack_shared_lib,
-                self.spec['lapack'].blas_shared_lib
-            ])
+            '@LIBS': (lapack + blas).joined()
         }
         #######
         # TODO : this part is replicated in PEXSI