Fix ambiguity and duplication in network install

As noted in the bug report, the initial paragraph confused where the
commands were to be run.

Additionally, database configuration is done in the 'configuring a
compute node' section, and was duplicated here.

Change-Id: If162d588f1d2c3eb85600c1cc481def9377ce94e
Backport: havana
Closes-Bug: 1256188
Merge "Fix ambiguity and duplication in network install"