Override getThreadPool from HystrixConcurrencyStrategy and delegate to

existing strategy if present. Fixes #2035

This allows clients to send batched up events in the same format as
before (or to continue to send single events). We can switch the
default format to an array in 1.4.x.

fixes a problem with whitespaces in list of retryable status codes

Merge branch 'fix_whitespaces_in_retryable_status_codes_list' of github.com:doernbrackandre/spring-cloud-netflix into fix_whitespaces_in_retryable_status_codes_list

This reverts commit f5524263.

Close response when retry on certain status codes

fixes gh-2028