Use of C++11 override keyword within standard and user code

[voertler]

In C++11 and newer the use of the override keyword is considered best practice. This should not affect the UVM user space i.e. means they should be free to use override as they like.
However, in UVM macros like UVM_OBJECT_UTILS should be used in user space to implement some virtual methods. The current macro implementation doesn't mark these as override. This leads to inconsistent override warnings when the user uses the override keyword in other parts of their classes.
I think there are 3 options to deal with this issue:

• Update the UVM macros to use override (LRM and Implementation issue UVM_OBJECT_UTILS macro defines non LRM method kind #288 needs to be fixed), this might trigger warnings in user space for users that have not used the override keyword (also regression tests)
• provide second macro which implements override
• advise users not to use override keyword in their classes

[SchulzSt]

VWG: update macros to use override keyword, update examples.

[voertler]

We also need to document this in the LRM.