Make sure that starting a qemu machine uses proper exponential backoffs
and that a single variable isn't shared across multiple backoffs.
DO NOT BACKPORT: I want to avoid backporting this PR to the upcoming 4.6
release as it increases the flakiness of machine start (see #17403). On
my M2 machine, the flake rate seems to have increased with this change
and I strongly suspect that additional/redundant sleep after waiting for
the machine to be running and listening reduced the flakiness. My hope
is to have more predictable behavior and find the sources of the flakes
soon.
[NO NEW TESTS NEEDED] - still too flaky to add a test to CI.
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>
732a02c57f