Introduce a context for RetryExponential

as second criteria (next to the maximum number of attempts) for canceling the retrying. This is required as we started with the previous commit to retry the nomad environment recovery. This always fails for unit tests (as they are not connected to an Nomad cluster). Before, we ignored the one error but the retrying leads to unit test timeouts.
Additionally, we now stop retrying to create a runner when the environment got deleted.

internal/environment/nomad_manager.go

@@ -36,6 +36,7 @@ func NewNomadEnvironmentManager(
 	runnerManager runner.Manager,
 	apiClient nomad.ExecutorAPI,
 	templateJobFile string,
+	ctx context.Context,
 ) (*NomadEnvironmentManager, error) {
 	if err := loadTemplateEnvironmentJobHCL(templateJobFile); err != nil {
 		return nil, err
@@ -43,7 +44,7 @@ func NewNomadEnvironmentManager(
 
 	m := &NomadEnvironmentManager{&AbstractManager{nil, runnerManager},
 		apiClient, templateEnvironmentJobHCL}
-	if err := util.RetryExponential(func() error { return m.Load() }); err != nil {
+	if err := util.RetryExponentialContext(ctx, func() error { return m.Load() }); err != nil {
 		log.WithError(err).Error("Error recovering the execution environments")
 	}
 	runnerManager.Load()