[KARAF-3192]Don't throw IllegalStateException when can't find attribute for a certain bean
(cherry picked from commit d05557f993e2f9a88330431de58b1fad19da167a)

Conflicts:
	management/server/src/main/java/org/apache/karaf/management/KarafMBeanServerGuard.java
(cherry picked from commit 0bf0ae657f69da5aafadd9d21769595ebd2754a7)