Mistral 2015.1 "2015.1"

This is the official OpenStack Kilo cycle release.

Implemented 34 blueprints, fixed 60 bugs.

The most important blueprints:

* "Join" flow control for direct workflows to synchronize multiple workflow branches (full and partial join patterns supported)
* Processing data collections using keyword "with-items" applicable for any workflow type
* Multitenancy support
* Actions now also have corresponding runtime objects, action executions, which allow to track workflow execution with any required granularity
* Workflow pause/resume
* Ability to kill workflows
* "pause-before" task policy (in conjunction with workflow resume feature allows to run workflows in "step-by-step" mode)
* Workflow environments
* YAQL expressions are now always defined in <% %> blocks
* Default workflow/action input parameter values
* Task policies are now defined without "policies" keyword
* Cron triggers now have time of the first occurrence and number of occurrences
* Validation of workflow/workbook DSL without uploading (separate endpoints)
* No-op tasks (e.g. can be used for synchronization of multiple workflow routes)
* Javascript action
* DB migrations
* Integration with Rally for benchmarking

The most noticable bugs fixed:

* Various concurrent issues in Mistral engine
* Cron trigger didn't work correctly with workflows using OpenStack actions (e.g. nova.servers_create)
* Concurrent issues in scheduler leading to making same delayed calls more than once
* Mistral couldn't store task results larger than 128kb
* "task-defaults" didn't work for reverse workflows
* SSL keystone authentication didn't work