cli: improve argument validation output

Improve the output for these validation errors:

- Removes the short command description from the output. This information
  does not provide much useful help, and distracts from the error message.
- Reduces punctuation, and
- Prefixes the error message with the binary / root-command name
  (usually `docker:`) to be consistent with other similar errors.
- Adds an empty line between the error-message and the "call to action"
  (`Run 'docker volume --help'...` in the example below). This helps
  separating the error message and "usage" from the call-to-action.

Before this patch:

    $ docker volume ls one two three
    "docker volume ls" accepts no arguments.
    See 'docker volume ls --help'.

    Usage:  docker volume ls [OPTIONS]

    List volumes

    $ docker volume create one two three
    "docker volume create" requires at most 1 argument.
    See 'docker volume create --help'.

    Usage:  docker volume create [OPTIONS] [VOLUME]

    Create a volume

With this patch:

    $ docker volume ls one two three
    docker: 'docker volume ls' accepts no arguments

    Usage:  docker volume ls [OPTIONS]

    Run 'docker volume ls --help' for more information

    $ docker voludocker volume create one two three
    docker: 'docker volume create' requires at most 1 argument

    Usage:  docker volume create [OPTIONS] [VOLUME]

    SRun 'docker volume create --help' for more information

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/network/connect_test.go

@@ -19,7 +19,7 @@ func TestNetworkConnectErrors(t *testing.T) {
 		expectedError      string
 	}{
 		{
-			expectedError: "requires exactly 2 arguments",
+			expectedError: "requires 2 arguments",
 		},
 		{
 			args: []string{"toto", "titi"},

cli/command/network/create_test.go

@@ -21,7 +21,7 @@ func TestNetworkCreateErrors(t *testing.T) {
 		expectedError     string
 	}{
 		{
-			expectedError: "exactly 1 argument",
+			expectedError: "1 argument",
 		},
 		{
 			args: []string{"toto"},

cli/command/network/disconnect_test.go

@@ -17,7 +17,7 @@ func TestNetworkDisconnectErrors(t *testing.T) {
 		expectedError         string
 	}{
 		{
-			expectedError: "requires exactly 2 arguments",
+			expectedError: "requires 2 arguments",
 		},
 		{
 			args: []string{"toto", "titi"},