(SERVER-246) Add :borrow-timeout config option

Add :borrow-timeout configuration option, which allows the user
to configure the timeout when borrowing instances from the JRuby
pool and defaults to 60000 milliseconds. Change all calls to
the borrow-from-pool function to calls to
borrow-from-pool-with-timeout.
The `get-in-config` function takes an optional default argument if the value isn't specified. You could just specify the `60000` there, but not a big deal.