virsh: Improve error message on integer value parsing failure.

Replace more than 30 ad-hoc error messages with a single, generic one
that contains the name of the option being processed and some hints
to help the user understand what could have gone wrong.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1207043

tools/virsh-domain-monitor.c

@@ -341,8 +341,9 @@ cmdDomMemStat(vshControl *ctl, const vshCmd *cmd)
      * This is not really an unsigned long, but it
      */
     if ((rv = vshCommandOptInt(cmd, "period", &period)) < 0) {
-        vshError(ctl, "%s",
-                 _("Unable to parse integer parameter."));
+        vshError(ctl,
+                 _("Numeric value for <%s> option is malformed or out of range"),
+                 "period");
         goto cleanup;
     }
     if (rv > 0) {
@@ -1439,8 +1440,9 @@ cmdDomTime(vshControl *ctl, const vshCmd *cmd)
 
     if (rv < 0) {
         /* invalid integer format */
-        vshError(ctl, "%s",
-                 _("Unable to parse integer parameter to --time."));
+        vshError(ctl,
+                 _("Numeric value for <%s> option is malformed or out of range"),
+                 "time");
         goto cleanup;
     } else if (rv > 0) {
         /* valid integer to set */