repo: Bump lock timeout to 5 minutes

repo: Bump lock timeout to 5 minutes

And update the doc text to talk about having a timeout at all
by default being a mistake.

Timeouts are really best handled at a higher level; if two processes
are contending for the ostree lock and one is actually frozen,
resolving this is something an admin may want to handle and introspect/debug
instead of having the waiter error out.

Most people using ostree are doing it in a way in which they have
higher level timeouts (e.g. on a container pod).