Fix wording for python3.4 section in the readme
Fix wording for python3.4 section in the readme

The python 3.4 section in the readme was a bit dated since we now also
test on python 3.5. This commit attempts to update the wording to
explain that it's python >=3.4 not just 3.4.

Change-Id: I32ebe4c278b1d5e25cd87ca03f7de1a265334610

sebrandon1/tempest,sebrandon1/tempest,Tesora/tesora-tempest,cisco-openstack/tempest,masayukig/tempest,cisco-openstack/tempest,masayukig/tempest,openstack/tempest,vedujoshi/tempest,Tesora/tesora-tempest,Juniper/tempest,vedujoshi/tempest,openstack/tempest,Juniper/tempest