use default_pool's spec when connecting in new process
use default_pool's spec when connecting in new process

prevents problems with the current_pool's spec overwriting
the default_pool in new process's, causing the master connection
to be actually the slave connection (if the slave was the
last current_pool, which it will be if :prefer_slave is on)

closes #CNVS-25288

Change-Id: I604519d706f37aa7318c0ceca22796a6645c6159
Reviewed-on: https://gerrit.instructure.com/67882
Reviewed-by: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
Tested-by: Jenkins
Product-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
QA-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>

instructure/switchman,instructure/switchman