Install Guide: Don't use obsolete sql_connection

For neutron and ceilometer, sql_connection is deprecated use
instead:
[database]
connection

Fixes some wrong format connection strings.

Also, reconnect_interval is deprecated in favor of retry_interval

Cherry-Pick: https://review.openstack.org/#/c/52832/
Change-Id: Ieb72349bafcbd1795d64f832d64fdbce695147bf
Backport: stable/havana
Partial-Bug: #1243131
Closes-Bug: #1205060
Merge "Install Guide: Don't use obsolete sql_connection" into stable/havana