Remove reference to py26 in tox testing instructions
Remove reference to py26 in tox testing instructions

Also change some rst formatting and clarify that tox
is used to run more than just *unit* tests.

Change-Id: I263af7b4f7a554da3a391cf5104af573c89e3825

revoer/keystone-8.0.0,aerwin3/swift,clayg/swift,prashanthpai/swift,prashanthpai/swift,openstack/swift,notmyname/swift,tipabu/swift,clayg/swift,matthewoliver/swift,tipabu/swift,notmyname/swift,smerritt/swift,revoer/keystone-8.0.0,swiftstack/swift,nadeemsyed/swift,nadeemsyed/swift,psachin/swift,openstack/swift,hurricanerix/swift,nadeemsyed/swift,openstack/swift,smerritt/swift,larsbutler/swift,psachin/swift,hurricanerix/swift,williamthegrey/swift,williamthegrey/swift,tipabu/swift,larsbutler/swift,hurricanerix/swift,psachin/swift,openstack/swift,redbo/swift,aerwin3/swift,swiftstack/swift,smerritt/swift,notmyname/swift,nadeemsyed/swift,tipabu/swift,hurricanerix/swift,swiftstack/swift,matthewoliver/swift,redbo/swift,notmyname/swift,matthewoliver/swift,clayg/swift,clayg/swift,psachin/swift,smerritt/swift,matthewoliver/swift