Added Sahara Image context

This context will be responsable for uploading and tagging an image for
Sahara clusters' benchmarks.

Change-Id: I9b89805e35f48212ac49ec94aa02ffc14d3ab535
Add db model and api for worker

The db model is called 'Worker', it's used to store the rally worker
service status. And the following db apis are added:
 * register_worker
 * get_worker
 * unregister_worker
 * update_worker

Change-Id: I38c792cc133dbace10eb7f2d4d202ca05ec7f9cc
Merge "Added Sahara Image context"
Adding sla_check to gate jobs

Adds proper sla checks to each benchmark configuration to be run
in the gates and adds sla check to the script to check if non-zero
status is returned

Change-Id: Ibba485aa1b070fc5eff0b4cfece0f249e9fae166
Renames *.rst files in /rally/doc/samples/tasks

Renames all .rst files in /rally/doc/samples/tasks
to README.rst.
And moves /rally/doc/samples/support to
/rally/doc/samples/tasks

Closes-bug: #1351599

Change-Id: I675266292bc1fbb62374ce0d12e6d06fbf7a8e3e
Merge "Adding sla_check to gate jobs"
Adds deleting scenarios for Neutron:

- NeutronNetwork.create_and_delete_networks

- NeutronNetwork.create_and_delete_subnets

- NeutronNetwork.create_and_delete_ports

blueprint benchmark-scenarios-for-neutron

Change-Id: I585b76935644712c019a9d5502637fbad6d4d2f0
Updated from global requirements

Change-Id: Ib4377d74f62035f6462669cdd257ae0f9140a637
Mock open to prevent file creation

Some unit tests does create files in root of project

Change-Id: I9b9907177ad1d25142d85538a727a5e8eab99df0
Update rally neutronclient ca_cert option

Recently the neutronclient constructor cacert parameter
has been changed to ca_cert causing rally gate failures.
Fixed it.

Neutron-client Change Id: I9d0395d405b9fbe4db08ad3727f9413be7b82811
Change-Id: Id616d0f315f247d4f89ee779c4424bc93cc208db
Closes-Bug:#1353268
Merge "Mock open to prevent file creation"
Amended sphinx documents

Change-Id: I520b08202910ad476447fa09ca0a5993fc1bffc5