This adds support for Erlang 17.0 and turns on itest tests

This includes:

* Bump pooler to version that supports Erlang 17.0
* Updates for R17 deprecation compatibility while maintaining
  backwards compatibility with R16 and R15
* Adds R15B03 to the Travis build list to verify it works
* Adds the itest target to the all make target to ensure integration
  tests are run as part of a fuill build