installDockerGeneric pipe masks curl failure, Docker install silently skipped #23760

Follow-up from review on #23716 (out of scope there per maintainer, tracked separately).

In pkg/libmachine/provision/utils.go, installDockerGeneric runs:

if ! type docker; then curl -fsSL | sh -; fi

Even with -f, when curl fails it outputs nothing, sh reads EOF, executes zero commands and exits 0. p.SSHCommand then returns nil error and minikube proceeds assuming Docker installed successfully, when it is not.

Suggested by Roslaan001 on #23716, either:

if ! type docker >/dev/null 2>&1; then curl -fsSL -o /tmp/install-docker.sh && sh /tmp/install-docker.sh && rm -f /tmp/install-docker.sh; fi

or verify after the pipeline:

if ! type docker >/dev/null 2>&1; then curl -fsSL | sh - && type docker >/dev/null 2>&1; fi

Related: #23709 (same unchecked-download bug class), #23716 (the -f flag, necessary but not sufficient here), #23719 (download-path test hardening).