python: make optimparallel package optional

Author: adamgeorge309

python/inet/simulation/optimize.py

@@ -1,8 +1,12 @@
 import math
-import optimparallel
 import scipy.optimize
 import time
 
+import importlib.util
+
+if importlib.util.find_spec('optimparallel'):
+    import optimparallel
+
 from omnetpp.scave.results import *
 
 from inet.simulation.config import *