Ensure token is a string

Token is passed as a header from wsgi to HTTPD
If that token is unicode, it triggers an exception in mod_wsgi

Closes-Bug: 1312971

Change-Id: I4bb6ef6c98fbcd35435956d701f1ee3281e9935a
(cherry picked from commit ba1bba8257716c2f5aa668e496173e96a80f0e43)