Fix package name for nova-spiceproxy on Ubuntu

Package name is nova-spiceproxy, not nova-spicehtml5proxy for Ubuntu.

Change-Id: Ica1e85f723c3deb1ec24134010de6c25c5f05e35
Closes-bug: #1257984
(cherry picked from commit 1134e8a17d827575c1c049d862d79dbbe08b7dbe)