sculpt: propagate managing_system role

This change allows for the hosting of system-management components
in Sculpt's runtime. The special role must be declared either as
<launcher managing_system="yes"> attribute or in the deploy
configuration's <start managing_system="yes"> attribute.

Issue #5009

repos/gems/run/sculpt.run

@@ -598,7 +598,7 @@ install_config {
 		</route>
 	</start>
 
-	<start name="runtime" caps="50000" priority="-1">
+	<start name="runtime" caps="50000" priority="-1" managing_system="yes">
 		<binary name="init"/>
 		<resource name="RAM" quantum="32G"/>
 		<resource name="CPU" quantum="40"/>

repos/gems/src/app/depot_deploy/child.h

@@ -426,6 +426,20 @@ void Depot_deploy::Child::gen_start_node(Xml_generator          &xml,
 				xml.attribute("priority", priority);
 		}
 
+		auto permit_managing_system = [&]
+		{
+			if (start_xml.attribute_value("managing_system", false))
+				return true;
+
+			if (_defined_by_launcher())
+				if (launcher_xml.attribute_value("managing_system", false))
+					return true;
+
+			return false;
+		};
+		if (permit_managing_system())
+			xml.attribute("managing_system", "yes");
+
 		bool shim_reroute = false;
 
 		/* lookup if PD/CPU service is configured and use shim in such cases */

repos/gems/src/app/sculpt_manager/deploy.h

@@ -167,6 +167,7 @@ struct Sculpt::Deploy
 					copy_attribute("cpu");
 					copy_attribute("priority");
 					copy_attribute("pkg");
+					copy_attribute("managing_system");
 
 					/* copy start-node content */
 					node.with_raw_content([&] (char const *start, size_t length) {