Fix Fleet log level integration test

Author: pchila

pkg/testing/fixture.go

@@ -665,6 +665,16 @@ func (f *Fixture) PrepareAgentCommand(ctx context.Context, args []string, opts .
 		return nil, fmt.Errorf("failed to prepare before exec: %w", err)
 	}
 
+	// prepare a client if it's not already set
+	if f.c == nil {
+		cAddr, err := control.AddressFromPath(f.operatingSystem, f.workDir)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get control protcol address: %w", err)
+		}
+		agentClient := client.New(client.WithAddress(cAddr))
+		f.setClient(agentClient)
+	}
+
 	// #nosec G204 -- Not so many ways to support variadic arguments to the elastic-agent command :(
 	cmd := exec.CommandContext(ctx, f.binaryPath(), args...)
 	for _, o := range opts {