Capture some variables in FlowMainEbos.

Make Opm::FlowMainEbos capture the variables argc, argv, outputCout, and
outputFiles. Passing the variables to the constructor and saving them as
class variables in Opm::FlowMainEbos makes the implementation of the
Python interface simpler. For example, the step_init() method does not
need to ask Opm::Main about the values of the variables when it needs to
run execute() in FlowMainEbos.

Another advantage of this refactoring could be that less variables needs
to be passed around from Opm::Main, to flow_ebos_xxx.cpp, and then again
to FlowMainEbos.

flow/flow_ebos_oilwater.cpp

@@ -85,8 +85,9 @@ int flowEbosOilWaterMain(int argc, char** argv, bool outputCout, bool outputFile
     Dune::MPIHelper::instance(argc, argv);
 #endif
 
-    Opm::FlowMainEbos<TTAG(EclFlowOilWaterProblem)> mainfunc;
-    return mainfunc.execute(argc, argv, outputCout, outputFiles);
+    Opm::FlowMainEbos<TTAG(EclFlowOilWaterProblem)>
+        mainfunc {argc, argv, outputCout, outputFiles};
+    return mainfunc.execute();
 }
 
 }