This change does a few things:
* Links live_migration_completion_timeout to the config
option guide.
* Links the force complete API reference to the feature support
matrix to see which drivers support the operation.
* Fixes the server status mentioned in the troubleshooting for
the force complete API reference (a live migrating server
status is MIGRATING, not ACTIVE). The same text is copied to the
abort live migration API reference troubleshooting for
consistency (and since using the server status is more natural than
the task_state).
* Links to the admin guide for troubleshooting live migration
timeouts.
Change-Id: I496d3f4b99e3d7e978c7ecb13ab3b67023fcb919
Closes-Bug: #1808579
18fbee57b4