[FIX] sap.m.NavContainer: Tests are now passing on IE11
[FIX] sap.m.NavContainer: Tests are now passing on IE11

Problem: There were remaining not destroyed Nav Container object, causing race
condition between instances.

Solution: we destroy it before running the problematic test

Change-Id: I32ae5c82bee01ecb91b76b31d39b53e80975447f
BCP: 2070068167

SAP/openui5,SAP/openui5,SAP/openui5,SAP/openui5