WellState FIBO: Return Segment Vectors from report()

This commit extends class WellStateFullyImplictBlackoil to report
segment-related quantities as Opm::data::Segment objects (included
in Opm::data::WellRates objects).  All wells have at least a top
segment in the context of WellState FIBO, so there is a meaningful
value to report for each well.

We put the extraction of segment-related quantities into a new
helper function

    WellStateFullyImplicitBlackoil::reportSegmentResults()

to avoid cluttering up the body of report() more than absolutely
needed.

The primary use-case for this is assigning appropriate values to
items 8 through 11 of restart vector RSEG.  In turn, this will
enable restoring these quantities from a restart file.

tests/test_wellstatefullyimplicitblackoil.cpp

@@ -74,8 +74,7 @@ namespace {
             setup.es, setup.sched, timeStep, *setup.grid.c_grid()
         };
 
-        state.init(wmgr.c_wells(), cpress, setup.sched,
-                   setup.sched.getWells(timeStep),
+        state.init(wmgr.c_wells(), cpress, setup.sched.getWells(timeStep),
                    timeStep, nullptr, setup.pu);
 
         state.initWellStateMSWell(wmgr.c_wells(), setup.sched.getWells(timeStep),