tests/qtest: Introduce qtest_resolve_machine_alias

tests/qtest: Introduce qtest_resolve_machine_alias

The migration tests are being enhanced to test migration between
different QEMU versions. A requirement of migration is that the
machine type between source and destination matches, including the
version.

We cannot hardcode machine types in the tests because those change
with each release. QEMU provides a machine type alias that has a fixed
name, but points to the latest machine type at each release.

Add a helper to resolve the alias into the exact machine
type. E.g. "-machine pc" resolves to "pc-i440fx-8.2"

Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <20231018192741.25885-6-farosas@suse.de>