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/gmsh/package.py

@@ -87,9 +87,9 @@ def install(self, spec, prefix):
         options.append('-DENABLE_OS_SPECIFIC_INSTALL=OFF')
 
         # Make sure GMSH picks up correct BlasLapack by providing linker flags
-        options.append('-DBLAS_LAPACK_LIBRARIES=%s %s' %
-                       (to_link_flags(spec['lapack'].lapack_shared_lib),
-                        to_link_flags(spec['blas'].blas_shared_lib)))
+        blas_lapack = spec['lapack'].lapack_libs + spec['blas'].blas_libs
+        options.append(
+            '-DBLAS_LAPACK_LIBRARIES={0}'.format(blas_lapack.ld_flags))
 
         # Gmsh does not have an option to compile against external metis.
         # Its own Metis, however, fails to build