_get_guest_config() is currently updating instance.root_device_name
and called in many ways like:
_hard_reboot(), rescue(), spawn(), resume(), finish_migration(),
finish_revert_migration()
It is an issue because root_device_name is initally set during instance
build and should remain the same after:
manager.py: _do_build_and_run_instance()
..
_default_block_device_names() <-here
..
driver.spawn()
This may lead to edge case, like in rescue where this value can be mistakenly
updated to reflect disk bus property of rescue image (hw_disk_bus).
Further more, a _get* method should not modify instance object.
Note that test test_get_guest_config_bug_1118829 is removed because no more
relevant with current code.
Change-Id: I1787f9717618d0837208844e8065840d30341cf7
Closes-Bug: #1835926
(cherry picked from commit 5e0ed5e7fe)
(cherry picked from commit 5e858d0cbd)
9f9f8d330a