Fix case where both docker and podman are installed, but docker is not podman alias

kernel.go

@@ -97,8 +97,7 @@ func (cmd *KernelDockerRegenCmd) Run(kernelCmd *KernelCmd, g *Globals) (err erro
 		}
 
 		args := []string{"build"}
-		_, err = exec.Command("which", "podman").CombinedOutput()
-		if err == nil {
+		if dockerIsPodman() {
 			args = append(args, "--squash-all")
 		}
 		args = append(args, "-t", d.ContainerName, imagePath)
@@ -353,8 +352,7 @@ func generateBaseDockerImage(registry string, commands []config.DockerCommand,
 	}
 
 	args := []string{"build"}
-	_, err = exec.Command("which", "podman").CombinedOutput()
-	if err == nil {
+	if dockerIsPodman() {
 		args = append(args, "--squash-all")
 	}
 	args = append(args, "-t", sk.DockerName(), imagePath)
@@ -427,8 +425,7 @@ func dockerImageAppend(sk config.KernelMask, pkgname string) (err error) {
 	}
 
 	args := []string{"build"}
-	_, err = exec.Command("which", "podman").CombinedOutput()
-	if err == nil {
+	if dockerIsPodman() {
 		args = append(args, "--squash-all")
 	}
 	args = append(args, "-t", sk.DockerName(), imagePath)
@@ -766,3 +763,11 @@ func generateKernels(km config.KernelMask, registry string,
 	}
 	return
 }
+
+func dockerIsPodman() bool {
+	output, err := exec.Command("docker", "version").CombinedOutput()
+	if err != nil {
+		return false
+	}
+	return strings.Contains(string(output), "podman")
+}