vfkit: More robust Kill()

We know that setting the state to `HardStop` typically fails:

    I0309 19:19:42.378591   21795 out.go:177] 🔥  Deleting "minikube" in vfkit ...
    W0309 19:19:42.397472   21795 delete.go:106] remove failed, will retry: kill: Post "http://_/vm/state": EOF

This may lead to unnecessary retries and delays. Fix by falling back to
sending a SIGKILL signal.

Example delete flow when setting vfkit state fails:

    I0309 20:07:41.688259   25540 out.go:177] 🔥  Deleting "minikube" in vfkit ...
    I0309 20:07:41.712017   25540 main.go:141] libmachine: Failed to set vfkit state to 'HardStop': Post "http://_/vm/state": EOF

Author: nirs

pkg/drivers/vfkit/vfkit.go

@@ -369,7 +369,27 @@ func (d *Driver) extractKernel(isoPath string) error {
 
 func (d *Driver) Kill() error {
 	if err := d.SetVFKitState("HardStop"); err != nil {
-		return err
+		// Typically fails with EOF due to https://github.com/crc-org/vfkit/issues/277.
+		log.Debugf("Failed to set vfkit state to 'HardStop': %s", err)
+		pidfile := d.pidfilePath()
+		pid, err := process.ReadPidfile(pidfile)
+		if err != nil {
+			if !errors.Is(err, os.ErrNotExist) {
+				return err
+			}
+			// No pidfile.
+			return nil
+		}
+		if err := process.Kill(pid, "vfkit"); err != nil {
+			if err != os.ErrProcessDone {
+				return err
+			}
+			// No process, stale pidfile.
+			if err := os.Remove(pidfile); err != nil {
+				log.Debugf("failed to remove %q: %s", pidfile, err)
+			}
+			return nil
+		}
 	}
 	return nil
 }