Install Guide: Use controller also for Ubuntu for sql_connection

We use for other distributions controller instead of localhost in
the connection string, use controller as well for Ubuntu

Change-Id: Ifd11c08300f10ed0dd50cd060afe03b3e6f18493
backport: havana
Closes-Bug: #1248603
(cherry picked from commit 56144af276484e11b0b69a1e0e6344e5006fb8cc)
Merge "Install Guide: Use controller also for Ubuntu for sql_connection" into stable/havana