Install Guide: Attempt to fix heat install

Heat install does not currently work.

This patch takes steps towards fixing it.

Use connection instead of sql_connection also for Ubuntu.
Markup fixes

Cherry-Pick: https://review.openstack.org/#/c/52582/
Backport: stable/havana
Closes-Bug: 1240396

Change-Id: I1d2ce9553667f6c3dace517c0f33219d35df9bc4
Install Guide: Enhance openSUSE/SLES Neutron install instructions

Add missing packages to install.
Start Open vSwitch by default on boot.

Cherry-Pick from:https://review.openstack.org/#/c/53433/
Change-Id: I3c0d236f324f2b8ffc3d81664b0658a5fedfdd3d
backport: havana
Closes-Bug: #1243131
Merge "Install Guide: Attempt to fix heat install" into stable/havana
Merge "Install Guide: Enhance openSUSE/SLES Neutron install instructions" into stable/havana