add spack post-installation testing

This Merge Request:

• adds or fixes tests for most EBRAINS (top-level) Spack packages
• adapts gitlab CI and installation script to run tests at installation time

packages/nest/package.py

@@ -198,6 +198,13 @@ class Nest(CMakePackage):
     @run_after('install')
     @on_package_attributes(run_tests=True)
     def installcheck(self):
+        print('''
+        ##########################################
+        ###
+        ### RUNNING MAKE INSTALLCHECK
+        ###
+        ##########################################
+''')
         with working_dir(self.build_directory):
             make("installcheck")