Do not specify a host for live-migration for non homogeneous nodes

In production cloud with non homogeneous compute nodes, specifying
a host for live-migration may fail unexpectedly, e.g., if source host
is with CPU "E5-2699 v4" and the selected target host is with CPU
"E5-2670 v3", the live-migration will fail because of the downgrade
issue.

So this is to add config option can_migrate_between_any_hosts which
can be set to False so that in non homogeneous cloud it can select
destination host automatically.

Change-Id: I05e9c8360b86326b7f58b2c0600fcb420bc31482
Closes-Bug: #1851185
diff --git a/releasenotes/notes/add-can-migrate-between-any-hosts-config-option-x8ah4f9737a28e9b.yaml b/releasenotes/notes/add-can-migrate-between-any-hosts-config-option-x8ah4f9737a28e9b.yaml
new file mode 100644
index 0000000..26fe01a
--- /dev/null
+++ b/releasenotes/notes/add-can-migrate-between-any-hosts-config-option-x8ah4f9737a28e9b.yaml
@@ -0,0 +1,9 @@
+---
+features:
+  - Add a new config option can_migrate_between_any_hosts in the
+    compute-feature-enabled section, which can be set to False for environment
+    with non homogeneous compute nodes, so that it can select a destination
+    host for migrating automatically, otherwise the testcase may fail
+    unexpectedly. e.g., if source host is with CPU "E5-2699 v4" and the
+    selected target host is with CPU "E5-2670 v3", the live-migration will
+    fail because of the downgrade issue.