Update requests version

A python-requests upgrade process was started before grizzly and was
planned to get into havana. Current projects don't depend on
requests<=1.1 anymore and this upgrade is needed in python-glanceclient.

Clients using python-requests are listed bellow:

Cinder:
https://github.com/openstack/python-cinderclient/blob/master/tools/pip-requires#L3
Nova:
https://github.com/openstack/python-novaclient/blob/master/tools/pip-requires#L4
Keystone:
https://github.com/openstack/python-keystoneclient/blob/master/tools/pip-requires#L4

Change-Id: I56c42eb7fdc5ac19736f125d3bffc52c9e26efee
Merge "Update requests version"