Full support of multiple hosts in transport url

This patch add the support of multiple hosts in transport url for rabbit and
qpid drivers. And also fix the amqp connection pool management to allow
to have one pool by transport.

Implements blueprint multiple-hosts-support-in-url

Co-Authored-By: Ala Rezmerita <ala.rezmerita@cloudwatt.com>
Change-Id: I5aff24d292b67a7b65e33e7083e245efbbe82024
Fix passing envelope variable as timeout

The envelope variable is being passed positionally in the timeout spot.

Change-Id: I64defdb0a9544d8c2ae69b38f723937b324ae504
Merge "Fix passing envelope variable as timeout"
Merge "Full support of multiple hosts in transport url"