migration: Fix migrate-to-same-host issue in bi-directional tests

[hholoubk]

Move migration_source_uri to top-level configuration to ensure it's always available when migrate_vm_back is enabled by CI overrides. This prevents the test from defaulting to qemu:///system (local host) during migration-back operations.

Changes:

• Add top-level migration_source_uri = "qemu+ssh://${client_ip}/system"
• Remove 4 redundant per-variant definitions in bi_directional cases

Resolves: LTF-823

AI assisted code and commit. Human reviewed.

Summary by CodeRabbit

• Chores
  • Refactored VM migration configuration by consolidating source URI settings to global scope, eliminating duplicate parameters from nested sections for simplified configuration management.

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[coderabbitai]

Walkthrough

This change consolidates the migration_source_uri configuration parameter from multiple nested configuration blocks into a single top-level global setting in the migration test configuration file. The parameter was previously defined in several nested locations under various migration scenarios (bi_directional blocks within p2p_migration and tunnelled_migration, as well as migration-with-nbd, gluster, and rdma sections) and is now centralized at the top level, eliminating duplication across four separate locations.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: moving migration_source_uri to top-level config to fix bi-directional migration tests, which directly addresses the changeset's primary objective.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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