Enhance Connection Collapse in ATS core

Add an option to support cache open read retry on a write lock
failure. With this option, as long as read-while-writer is set
up following the guidelines in the docs, there should be no need
for any plugins to augment the core. Eventual plan is to deprecate
collapsed_forwarding plugin with this new support.

For more context on this, see
https://cwiki.apache.org/confluence/display/TS/Presentations+-+2019?preview=/112821251/132320653/Collapsed%20Forwarding%20.pdf
5 files changed