(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.
I think I'm good with an exception being thrown here as opposed to having the caller check for nil, although I'd prefer to make it more generic since `NullPointerException` wouldn't seem to be meaningful to the caller.  Also, I think it would be good to document in the macro that the exception could be thrown in the event that a timeout expired when trying to get the instance.  @KevinCorcoran what do you think?