Add oslo.serialization

Add the new Oslo library for managing object serialization. This code is
moving out of the incubator into a library, so projects that wish to
continue using it need the requirement added to the global list first.

NOTE: this is needed for clients installed from master using oslo.serialization.

Conflicts:
	global-requirements.txt

Partial-Bug: #1366748

Change-Id: Iff29ce2e88cddc2332229cfbbc518251dd2c76f3
(cherry picked from commit 2ce3f8259b56410bdd73deca09b7963f4a46e1da)