Command-line input validation: reject unused args

Several podman commands accept no subcommands. Some
of those were not actually checking, though, which
could lead to user confusion. Added validation where
missing; and, refactored to minimize duplication.

(Side note: I decided against using cobra.NoArgs
because its error message, "unknown command",
misleadingly implies that there are known ones).

Also added validation to varlink

Signed-off-by: Ed Santiago <santiago@redhat.com>

cmd/podman/version.go

@@ -17,6 +17,7 @@ var (
 	versionCommand  cliconfig.VersionValues
 	_versionCommand = &cobra.Command{
 		Use:   "version",
+		Args:  noSubArgs,
 		Short: "Display the Podman Version Information",
 		RunE: func(cmd *cobra.Command, args []string) error {
 			versionCommand.InputArgs = args