Disconnect from master after write operation

We want the MSA to disconnect from the master after a write operation. The
adapter exposes the `wait_timeout` configuration setting. However, the setting
does not work as advertised.

This quick n' dirty hack tells the database to close the connection after a
arbitrary 1 second idle timeout expires. Calling disconnect! on the adapter
connection nullifies the underlying raw_connection causing subsequent accesses
to the master_connection to fail. This is slightly cleaner as it uses baked in
rails/activerecord logic to reconnect to the database.

This should result in considerably less idle connections on the datbase master,
thus reducing database context switch overhead.

Change-Id: I83e90565aeba73d590bb1d661b5b6da8c76e53ac
Reviewed-on: https://gerrit.causes.com/19236
Reviewed-by: John Skopis <john.skopis@causes.com>
Tested-by: John Skopis <john.skopis@causes.com>