Move location of HTTPException in swift_testing

While doing some work around swiftclient Python 3 support, httplib
imports were changed to use six.moves in order to access httplib in Py2
and http.client in Py3. Tests related to those changes are failing
because these functional tests are depending on HTTPException being
a name in swiftclient.client. These tests should acces that name from
its canonical location in httplib (or, eventually, a Py3 friendly
location like six.moves).

Change-Id: I6335d465574045daedab47e5fe23c415d171a83a
Merge "Move location of HTTPException in swift_testing"