docker: increase database connection timeout

docker: increase database connection timeout

When starting the Docker environment, if the web container can't see the
database immediately, it waits 5 seconds, tries again, then waits 15
seconds more to account for first-time start-ups where it takes a bit
longer for the database to be initialised.

Some of us, unfortunately, have slow computers with slow mechanical hard
drives which take just a bit longer. Increase the second timeout from 15
seconds to 60 seconds, testing every 5 seconds.

Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Stephen Finucane <stephen@that.guru>