Drop greenio dependency

greenio dependency was added to add a new "greenio executor" to Oslo
Messaging, but I abandonned the changeset:
https://review.openstack.org/#/c/108652/

No OpenStack component use greenio.

Change-Id: I6a97e3b462f8d0985532384ea169ebee4c9b3c2d
Depend on any 0.9.x SQLAlchemy that is >= 0.9.7

Drop the 0.8.x series of SQLAlchemy which makes the SQLAlchemy
simpler and ensures that it doesn't depend on an implementation
detail of setuptools. This is important because a future version
of setuptools (8.0) and pip (6.0) plan to change this implementation
detail.

Change-Id: I2f13918c169071d4365c689bdb709a04064279fa
Merge "Drop greenio dependency"
Merge "Depend on any 0.9.x SQLAlchemy that is >= 0.9.7"
Add oslo.context

allow projects to use the new oslo.context instead of copying
context.py from oslo-incubator. This is needed for getting the
initial version of oslo.log out as well.

Implements: blueprint graduate-oslo-context
Change-Id: Ieda867c672ea627f7d1e5f7dfc018624ba374fd6
Merge "Add oslo.context"