BeanManagerProvider.isActive() returns true after container shutdown

While trying to implement DELTASPIKE-1197 I found that BeanManagerProvider.isActive() returns true after container shutdown.

The javadocs for isActive() say "@return true if the BeanManagerProvider is ready to be used", but when it is in this state, the BeanManagerProvider can't actually be used because the CDI container is not active.

In the case of Weld, when BeanProvider.getContextualReference() was called I got errors like "java.lang.IllegalStateException: Singleton not set for STATIC_INSTANCE => []". There was no stack trace, but that message comes from Weld's RegistrySingletonProvider.java.

It would seem reasonable to reset bmpSingleton to null during cleanupStoredBeanManagerOnShutdown, but for some reason this breaks a lot of tests.