Reduce number of processes (#1832)

* Refactor code

* Edit tox

* Modify tox

* Modify tests

* Reduce processes

* Reduce processes

tests/integration_tests/parallel_test.py

@@ -9,7 +9,7 @@ def test_parallel():
 
     test_file = str(TESTDATA / "input_contracts" / "origin.sol")
     program = f"python3 {MYTH} a {test_file} --solv 0.5.0 -o json"
-    processes = [Popen(program, stdout=PIPE, shell=True) for i in range(8)]
+    processes = [Popen(program, stdout=PIPE, shell=True) for i in range(4)]
     for p in processes:
         out, err = p.communicate()
         json_output = json.loads(out.decode("utf-8"))