BrainScaleS: Provide run environment in install tests

Install tests don't seem to use the environment provided by
`def setup_run_environment(…)`; we work around by providing the
necessary PYTHONPATH environment variable manually.

packages/hxtorch/package.py

@@ -176,4 +176,6 @@ class Hxtorch(WafPackage):
 
     def install_test(self):
         with working_dir('spack-test', create=True):
+            old_pythonpath = os.environ.get('PYTHONPATH', '')
+            os.environ['PYTHONPATH'] = ':'.join([str(self.prefix.lib), old_pythonpath])
             python('-c', 'import hxtorch; print(hxtorch.__file__)')

packages/pynn-brainscales/package.py

@@ -153,4 +153,6 @@ class PynnBrainscales(WafPackage):
 
     def install_test(self):
         with working_dir('spack-test', create=True):
+            old_pythonpath = os.environ.get('PYTHONPATH', '')
+            os.environ['PYTHONPATH'] = ':'.join([str(self.prefix.lib), old_pythonpath])
             python('-c', 'import pynn_brainscales; print(pynn_brainscales.__file__)')