During the transformation of nova-compute to native threading mode we made a shortcut to fit into the Gazpacho timeline. We moved the build and snapshot operations to the same long task executor and we simplified the limit handling to have a single shared limit for the two task types. We should restore the per task type limit by extending the futurist. Executor with per task type limit handling.

This shared limit handling also prevented us to move the live-migration task to the long task executor. After the refactor we should move it there too.

Acceptance criteria:

• Extend futurist lib to have an Executor that support per task type concurrency limits
• Restore the independent build and snapshot concurrency limits in nova based on the new futurist functionality.
• Move live-migartion to the long-task executor