Fixed apt-repo on host to be served on port 8090

Switched from port 8080 which is being used by swift-proxy
in the devstack-vm-gate scripts to port 8090. The guest
now connects to the host apt-repo on port 8090 to download
the my.cnf file.

Fixes bug: 1117080

Change-Id: I2efcf715b426a3e6d5caaf09729926714cb1a08d