Forbid running install steps on stage 0

Author: Kobzol

src/bootstrap/src/core/config/config.rs

@@ -1045,6 +1045,10 @@ impl Config {
                 eprintln!("ERROR: cannot dist anything on stage 0. Use at least stage 1.");
                 exit!(1);
             }
+            (0, Subcommand::Install { .. }) => {
+                eprintln!("ERROR: cannot install anything on stage 0. Use at least stage 1.");
+                exit!(1);
+            }
             _ => {}
         }