Install Guide: configure the neutron metadata agent

VMs won't be able to access the metadata API if the Neutron metadata
agent is not configured.

closes-bug: #1252521
closes-bug: #1252522
backport: havana
Change-Id: I531f04a2a972b7f9e5ddc1508afac752c01ab563
(cherry picked from commit e67a5a19d0dd89d771ecde7b2b8e82ee8e79a396)
Install Guide: Improve nova compute install

Move the sqlite removal step last - after restart of the nova service.
Remove duplicate "Edit nova.conf" line on Ubuntu

Change-Id: I66de794b38a59eadf446954f1d7f6ef43f415ba7
Closes-Bug: #1251710
backport: havana
(cherry picked from commit 5dadd35a3c0ecf99fadf81c73af4a37abc8a71ab)
Merge "Install Guide: configure the neutron metadata agent" into stable/havana
Merge "Install Guide: Improve nova compute install" into stable/havana