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/py-scipy/package.py

@@ -47,7 +47,7 @@ def install(self, spec, prefix):
             env['ATLAS'] = join_path(
                 spec['atlas'].prefix.lib, 'libatlas.' + dso_suffix)
         else:
-            env['BLAS']   = spec['blas'].blas_shared_lib
-            env['LAPACK'] = spec['lapack'].lapack_shared_lib
+            env['BLAS'] = spec['blas'].blas_libs.joined()
+            env['LAPACK'] = spec['lapack'].lapack_libs.joined()
 
         python('setup.py', 'install', '--prefix=%s' % prefix)