Investigate why we had to forbid operation interruption

During investigation of regression introduced with fix of WFCORE-6156
I noticed the awaitStability() was interrupted (in OperationContextImpl.releaseStepLocks() method) and
that interruption left server in inconsistent state. Later it led to test suite regression (see WFCORE-6157 for list of regressions).

The purpose of this JIRA is to identify why we had to forbid interruption of thread executing the operation (see WFCORE-6157)
There are at least two possibilities:
1) Some test didn't cleanup the environment properly and that caused some tests following it to regress
2) We have to forbid operation cancellation (this is effective now) because it is dangerous operation as it can leave server in inconsistent state.

If second option is the case then also timeout of operation execution is a potential huge problem.