Use byte string or utf8 depending on python version for wsgi
Use byte string or utf8 depending on python version for wsgi

A recent change to the wsgi code broke deployments running over
httpd/mod_wsgi. This is because for py2.X mod_wsgi accepts byte
strings and breaks with utf8. However, for py3.X, utf8 is
accepted. So this acts accordingly.

Change-Id: I81739bc3de9d623b718987b5fc18eaf851533902
Closes-Bug: #1643511

jianghuaw/nova,klmitch/nova,gooddata/openstack-nova,rahulunair/nova,openstack/nova,klmitch/nova,klmitch/nova,mahak/nova,openstack/nova,Juniper/nova,mahak/nova,hanlind/nova,Juniper/nova,gooddata/openstack-nova,phenoxim/nova,openstack/nova,Juniper/nova,hanlind/nova,klmitch/nova,vmturbo/nova,vmturbo/nova,phenoxim/nova,gooddata/openstack-nova,rajalokan/nova,mikalstill/nova,mikalstill/nova,rahulunair/nova,jianghuaw/nova,rajalokan/nova,Juniper/nova,mahak/nova,rahulunair/nova,jianghuaw/nova,mikalstill/nova,vmturbo/nova,gooddata/openstack-nova,hanlind/nova,vmturbo/nova,jianghuaw/nova,rajalokan/nova,rajalokan/nova