Adds nova-api-metadata to Ubuntu instructions for nova-network

backport: havana
Change-Id: I5d5dbc7320acbb19ae2c227057dde4081d420af3
Fix-bug: 1263752
(cherry picked from commit 28c2e9e2bf1b8dd7df039478566b8a923994c6c9)
Merge "Adds nova-api-metadata to Ubuntu instructions for nova-network" into stable/havana