Fixing flake8 warnings and errors

flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics --exclude benchmark

Excluding the benchmark directory (due to protobuf generated files)
Also removing some Python2 specific code

scripts/capnp_test_pycapnp.py

@@ -1,12 +1,13 @@
 #!/usr/bin/env python
 from __future__ import print_function
-import capnp
 import os
+import sys
+
+import capnp
 capnp.add_import_hook([os.getcwd(), "/usr/local/include/"]) # change this to be auto-detected?
 
-import test_capnp
+import test_capnp # noqa: E402
 
-import sys
 
 def decode(name):
     class_name = name[0].upper() + name[1:]
@@ -18,6 +19,7 @@ def encode(name):
     message = getattr(test_capnp, class_name).from_dict(val.to_dict())
     print(message.to_bytes())
 
+
 if sys.argv[1] == 'decode':
     decode(sys.argv[2])
 else: