Bump python-savannaclient version to >=0.4.1

There are several reasons because we'd like to do it:

* it includes support for all features that'll be released in i-2;
* and, so, we'd like to use it to update Horizon plugin with new features;
* there are several fixes that blocks usage of client in Heat and Tempest;
* it contains basic implementation of CLI that we'd like to test in Tempest.

Change-Id: If46cbc1aeaa970b5b3d1066a83ea9b22f9d0ea49
Remove oauth2 requirement

Since this patch was merged: https://review.openstack.org/#/c/64427/
Keystone now uses oauthlib instead of oauth2 as it's library for
OAuth related functions.

The previous oauth2 lib can now be removed from the global
requirements

Change-Id: Iba4beddc8d6e62d1657b68740fcca9d9a8fc7351
nova api validation fw requires jsonschema >= 2.0.0

The new nova api validation framework for v3 api uses methods (eg.
validators.extend) in jsonschema which are available starting in
version 2.0.0. The current min version is 1.3.0 and is incompatible
with the latest changes.

Change-Id: I943fd68b9fab3bce1764305a5058df5339470757
Partial-Bug: #1256344
Merge "nova api validation fw requires jsonschema >= 2.0.0"
Merge "Remove oauth2 requirement"
Merge "Bump python-savannaclient version to >=0.4.1"