Improved error messaging for plugin unload

Changed the error message to more appropriate one for `plugin swap` when ver < 1

cmd/snaptel/plugin.go

@@ -66,19 +66,24 @@ func loadPlugin(ctx *cli.Context) error {
 func unloadPlugin(ctx *cli.Context) error {
 	pType := ctx.Args().Get(0)
 	pName := ctx.Args().Get(1)
-	pVer, err := strconv.Atoi(ctx.Args().Get(2))
+	pVerStr := ctx.Args().Get(2)
 
 	if pType == "" {
 		return newUsageError("Must provide plugin type", ctx)
 	}
 	if pName == "" {
 		return newUsageError("Must provide plugin name", ctx)
 	}
+	if pVerStr == "" {
+		return newUsageError("Must provide plugin version", ctx)
+	}
+
+	pVer, err := strconv.Atoi(pVerStr)
 	if err != nil {
 		return newUsageError("Can't convert version string to integer", ctx)
 	}
 	if pVer < 1 {
-		return newUsageError("Must provide plugin version", ctx)
+		return newUsageError("Plugin version must be greater than zero", ctx)
 	}
 
 	r := pClient.UnloadPlugin(pType, pName, pVer)
@@ -139,7 +144,7 @@ func swapPlugins(ctx *cli.Context) error {
 		return newUsageError("Must provide plugin name", ctx)
 	}
 	if pVer < 1 {
-		return newUsageError("Must provide plugin version", ctx)
+		return newUsageError("Plugin version must be greater than zero", ctx)
 	}
 
 	r := pClient.SwapPlugin(paths, pType, pName, pVer)