mixedversion: don't mark shared process tenant availability in monitor

The monitor does not support monitoring shared process tenants
in isolation, i.e. it can only monitor both system and the
secondary shared process.

However, the mixed version framework was reporting availability of
shared process tenants to the monitor. This broke an assumption that
the monitor makes that any registered process is either the system
tenant or a separate process tenant. This would cause the monitor to
mistakenly believe there was a running separate process tenant.

Author: DarrylWong

pkg/cmd/roachtest/roachtestutil/mixedversion/helper.go

@@ -97,13 +97,19 @@ func (s *Service) RandomDB(rng *rand.Rand) (int, *gosql.DB) {
 	return node, s.Connect(node)
 }
 
-// prepareQuery returns a connection to one of the `nodes` provided
-// and logs the query and gateway node in the step's log file. Called
+// prepareQuery returns a connection to one of the available nodes in `nodes`
+// provided and logs the query and gateway node in the step's log file. Called
 // before the query is actually performed.
 func (s *Service) prepareQuery(
 	rng *rand.Rand, nodes option.NodeListOption, query string, args ...any,
 ) (*gosql.DB, error) {
 	availableNodes := s.AvailableNodes().Intersect(nodes)
+	if len(availableNodes) == 0 {
+		return nil, errors.Newf(
+			"no available nodes in the intersection of %s and %s",
+			s.AvailableNodes(), nodes,
+		)
+	}
 	node := availableNodes.SeededRandNode(rng)[0]
 	db := s.Connect(node)
 
@@ -137,8 +143,7 @@ func (s *Service) Exec(rng *rand.Rand, query string, args ...interface{}) error
 func (s *Service) ExecWithGateway(
 	rng *rand.Rand, nodes option.NodeListOption, query string, args ...interface{},
 ) error {
-	availableNodes := s.AvailableNodes().Intersect(nodes)
-	db, err := s.prepareQuery(rng, availableNodes, query, args...)
+	db, err := s.prepareQuery(rng, nodes, query, args...)
 	if err != nil {
 		return err
 	}

pkg/cmd/roachtest/roachtestutil/mixedversion/steps.go

@@ -903,7 +903,7 @@ func (s networkPartitionInjectStep) Run(
 	ctx context.Context, l *logger.Logger, _ *rand.Rand, h *Helper,
 ) error {
 	h.runner.monitor.ExpectProcessDead(s.targetNode)
-	if h.Tenant != nil {
+	if h.DeploymentMode() == SeparateProcessDeployment {
 		opt := option.VirtualClusterName(h.Tenant.Descriptor.Name)
 		h.runner.monitor.ExpectProcessDead(s.targetNode, opt)
 	}
@@ -958,7 +958,7 @@ func (s networkPartitionRecoveryStep) Run(
 	}
 
 	h.runner.monitor.ExpectProcessAlive(s.targetNode)
-	if h.Tenant != nil {
+	if h.DeploymentMode() == SeparateProcessDeployment {
 		opt := option.VirtualClusterName(h.Tenant.Descriptor.Name)
 		h.runner.monitor.ExpectProcessAlive(s.targetNode, opt)
 	}