Remove unnecessary str() which was for XML
Remove unnecessary str() which was for XML

Tempest has dropped XML support and the removed str() becames
meaningles. So this patch removes it.

Change-Id: I02184d725d40417d501f0dc57eb1977bffc77f72

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