add kubectl check for ko delete, apply, and create (#120)

pkg/commands/commands.go

@@ -15,6 +15,8 @@
 package commands
 
 import (
+	"os/exec"
+
 	"github.com/spf13/cobra"
 )
 
@@ -31,3 +33,11 @@ func AddKubeCommands(topLevel *cobra.Command) {
 	addRun(topLevel)
 	addCompletion(topLevel)
 }
+
+// check if kubectl is installed
+func isKubectlAvailable() bool {
+	if _, err := exec.LookPath("kubectl"); err != nil {
+		return false
+	}
+	return true
+}