Accept multi machine_types for /nodes/lock_many/

... separated byt '|'

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Add /nodes/?count=X

With test. X must be an int, of course.

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Add Run.next_job_id

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Generate a new job_id if necessary

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Be aware of job_id generation

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>