Wrong proxy port for Spice proxy

If we look at nova/cmd/spicehtml5proxy.py, we use 6082 port for Spice proxy.

In nova.conf, the default port for html5proxy_base_url is 6080 which fails console
service.

Fix bug #1172957

See also https://review.openstack.org/#/c/27524/

Change-Id: I3d7df3bfc7e0520024bbbe409aa9ae5735982f9e