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