Ask the running runtimes where they keep their data, and read every form a unit says it in

The third review of #64 (hq issue 339): an ExecStart continued over lines, a
quoted path, a variable from Environment= or EnvironmentFile= across the unit
and its drop-ins, dockerd's --config-file and podman's TOML literal strings
each hid a data root from the guard. The running runtimes are now asked first
(docker info, podman info) on a runner of the guard's own, and the files are
read beside them in all those forms.

cmd/mesh-host/main.go

@@ -232,6 +232,8 @@ func run(ctx context.Context, command string, opts options) error {
 	// found (novox/hq issue 339).
 	handedOverFrom(opts.state)
 	foundState.Store(opts.state)
+	// And the guard asks the running container runtimes where they keep their data (novox/hq issue 339).
+	apply.AskRuntimes = apply.ExecRunner
 	switch command {
 	case "hand-over":
 		return handOverCommand(opts)