(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.
(SERVER-246) Improve Error handling after timeout

Improve the error handling in the `with-jruby-puppet` macro
when borrowing an instance from the pool times out.
Merge pull request #329 from fpringvaldsen/SERVER-246-change-borrows

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