Drop neutron.common.rpc.MessagingTimeout

Drop the last neutron.common.rpc exception mapping, MessagingHelper,
which wasn't actually used anywhere anyway.

Part of blueprint drop-rpc-compat.

Change-Id: I43b9b97accff9cc7684146076ba0b5d62302f06e
switch to oslo.serialization

jsonutils has been moved to the oslo.serialization library. in this
patch we bring in oslo.serialization and switch all references to
the new library.

Closes-Bug: #1385353
Change-Id: I2898c4040abb2f208959049708e7bc093cfbaba7
enable F811 check for flake8

This change incorporates two cleanups that do not change logic:
- Removes the shadowed unused imports by using the proper oslo.config import
mechanism
- duplicate unit tests have been removed
- duplicate unit test names have been corrected to reflect true test
  nature

Change-Id: Iad7a3373c1f787a2078b932c5f40bb718ad76767
Partial-Bug: 1329017
Merge "Drop neutron.common.rpc.MessagingTimeout"
Merge "switch to oslo.serialization"
Merge branch 'master' of https://github.com/openstack/quantum