Update requests requirements

Bump the version requirements for requests so it does
not conflict with the version of requests required
for glance (unpinned).

Change-Id: I06479b8ceb04df749a6d7f7dc584892a688cd449
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Pin requests module more strictly.

requests.request() does not accept the keyword argument 'config'
(used on keystoneclient/client.py:339) after version 1.0.0.

Fixes bug #1116740

Change-Id: I0a778849ff44a76a2647aa46057fdb35401fae5f