Do not allow OpenBLAS/numpy to run multithreaded

python/dune/perftool/__init__.py

+# Disallow numpy to use multithreading - it breaks parallel code generation
+# on machines with large core count.
+import os
+os.environ["OMP_NUM_THREADS"] = 1
+
 # Trigger imports that involve monkey patching!
 import dune.perftool.loopy.symbolic