release v1.15.0

update kubernetes version

release latest snapshot image/iso

Rename `out.T` to `out.Step`

fix Test flakes TestAddons/parallel/Registry

Implement schedule stop for unix

automatically try install kvm for kvm2 tests

Use special credential file location for cloud shell

Don't check for docker.io prefix in docker preload

Right now, preload isn't working because it thinks that the
kubernetes/dashboard images don't exist. This is because they now have a
docker.io prefix introduced by 4c54e786

Since `docker images` won't return image names with that prefix, we want
to strip the images of `docker.io` before checking if they exists in the
docker daemon.

This also fixes the TestPause/serial/SecondStartNoReconfiguration
failing integration test.

Fix failing TestJSONOutput/start test

icrease gh action timeout for macos

add --watch flag for minikube status with optional interval duration

Improve parsing of start flag apiserver-names