Add beanstalk as a possible queue backend for Teuthology Jobs along with Paddles

Add beanstalk as a possible queue backend for Teuthology Jobs along with Paddles

With the use of the --queue-backend argument the user can specify which backend(paddles/beanstalk) they would like to use for maintaining the teuthology Jobs queue.
In order to avoid overlapping Job IDs, when a job is being scheduled in beanstalk it is also written to paddles which returns a unique ID.
This is the ID teuthology will treat as the Job ID throughout the run of the job.

To differentiate between the 2 queue backends, the teuthology-queue command has been split into teuthology-paddles-queue command and teuthology-beanstalk-queue command.

Signed-off-by: Aishwarya Mathuria <amathuri@redhat.com>