ENH: add -verbose support into argList

- similar to -dry-run handling, can be interrogated from argList,
  which makes it simpler to add into utilities.

- support multiple uses of -dry-run and -verbose to increase the
  level. For example, could have

    someApplication -verbose -verbose

 and inside of the application:

    if (args.verbose() > 2) ...

BUG: error with empty distributed roots specification (fixes #2196)

- previously used the size of distributed roots to transmit if the
  case was running in distributed mode, but this behaves rather poorly
  with bad input. Specifically, the following questionable setup:

      distributed true;
      roots ( /*none*/ );

  Now transmit the ParRunControl distributed() value instead,
  and also emit a gentle warning for the user:

      WARNING: running distributed but did not specify roots!

applications/utilities/preProcessing/setExprFields/setExprFields.C

@@ -553,9 +553,8 @@ int main(int argc, char *argv[])
     (
         "Evaluate but do not write"
     );
-    argList::addBoolOption
+    argList::addVerboseOption
     (
-        "verbose",
         "Additional verbosity",
         true // Advanced option
     );
@@ -662,9 +661,6 @@ int main(int argc, char *argv[])
 
     #include "createTime.H"
 
-    const bool dryrun = args.dryRun();
-    const bool verbose = args.found("verbose");
-
     const word dictName("setExprFieldsDict");
 
     instantList times = timeSelector::select0(runTime, args);
@@ -797,7 +793,7 @@ int main(int argc, char *argv[])
 
             setExprFieldsControl ctrl;
 
-            ctrl.dryRun = dryrun;
+            ctrl.dryRun = args.dryRun();
             ctrl.debugParsing = args.found("debug-parser");
             ctrl.cacheVariables = !args.found("no-variable-caching");
 
@@ -869,7 +865,7 @@ int main(int argc, char *argv[])
 
                 setExprFieldsControl ctrl;
 
-                ctrl.dryRun = dryrun;
+                ctrl.dryRun = args.dryRun();
                 ctrl.debugParsing = args.found("debug-parser");
                 ctrl.cacheVariables = !args.found("no-variable-caching");
 
@@ -934,7 +930,7 @@ int main(int argc, char *argv[])
                     ctrl.useDimensions = bool(dimPtr);
                 }
 
-                if (verbose && !timei)
+                if (args.verbose() && !timei)
                 {
                     // Report once
                     Info<< "Processing" << dict << nl;