flow_ebos: print statistics about failed time steps

the performance summary at the end of a Norne run which are printed by
`flow_ebos` now looks like this on my machine:

```
Total time (seconds):         773.757
Solver time (seconds):        753.349
 Assembly time (seconds):     377.218 (Failed: 23.537; 6.23965%)
 Linear solve time (seconds): 352.022 (Failed: 23.2757; 6.61201%)
 Update time (seconds):       16.3658 (Failed: 1.13149; 6.91375%)
 Output write time (seconds): 22.5991
Overall Well Iterations:      870 (Failed: 35; 4.02299%)
Overall Linearizations:       2098 (Failed: 136; 6.48236%)
Overall Newton Iterations:    1756 (Failed: 136; 7.74487%)
Overall Linear Iterations:    26572 (Failed: 1786; 6.72136%)
```

for the flow_legacy family, nothing changes.

opm/polymer/SimulatorPolymer.hpp

@@ -20,6 +20,7 @@
 #ifndef OPM_SIMULATORPOLYMER_HEADER_INCLUDED
 #define OPM_SIMULATORPOLYMER_HEADER_INCLUDED
 
+#include <opm/core/simulator/SimulatorReport.hpp>
 #include <boost/shared_ptr.hpp>
 #include <vector>
 
@@ -95,8 +96,18 @@ namespace Opm
                             PolymerState& state,
                             WellState& well_state);
 
+        /// return the statistics if the nonlinearIteration() method failed.
+        ///
+        /// NOTE: for the flow_legacy simulator family this method is a stub, i.e. the
+        /// failure report object will *not* contain any meaningful data.
+        const SimulatorReport& failureReport() const
+        { return failureReport_; }
+
     private:
         class Impl;
+
+        SimulatorReport failureReport_;
+
         // Using shared_ptr instead of scoped_ptr since scoped_ptr requires complete type for Impl.
         boost::shared_ptr<Impl> pimpl_;
     };