Cleanup of Network Guide: app_demo_multi_dhcp_agents

This is a minor cleanup, focussing on markup.

Change-Id: I0ebc024af4c7b9431f5553395213039c27371eec
Fix postgresql install doc for RHEL/Centos

As noted in the bug report, the package listed in the doc
did not exist. Replaced it with the correct one.

Change-Id: Id0d59e32e696090604a9ad8fb8ba6140afd89c56
Closes-Bug: 1214886
Merge "Cleanup of Network Guide: app_demo_multi_dhcp_agents"
Merge "Fix postgresql install doc for RHEL/Centos"