Remove some required properties from schemas.

They are still required, but it's not really possible run the schemas without these properties being there

plugins/prebootstrapped/manifest-schema.json

@@ -27,9 +27,8 @@
 						}
 					}
 				}
-			},
+			}
-			"required": ["prebootstrapped"]
 		}
 	},
-	"required": ["volume", "plugins"]
+	"required": ["volume"]
 }

plugins/root_password/manifest-schema.json

@@ -15,9 +15,7 @@
 					},
 					"required": ["password"]
 				}
-			},
+			}
-			"required": ["root_password"]
 		}
-	},
+	}
-	"required": ["plugins"]
 }