add an implement for calicoctl version --client

Signed-off-by: cyclinder <qifeng.guo@daocloud>

calicoctl/calicoctl/commands/version.go

@@ -46,7 +46,7 @@ func init() {
 
 func Version(args []string) error {
 	doc := `Usage:
-  <BINARY_NAME> version [--config=<CONFIG>] [--poll=<POLL>] [--allow-version-mismatch]
+  <BINARY_NAME> version [--config=<CONFIG>] [--poll=<POLL>] [--allow-version-mismatch] [--client]
 
 Options:
   -h --help                    Show this screen.
@@ -56,6 +56,8 @@ Options:
      --poll=<POLL>             Poll for changes to the cluster information at a frequency specified using POLL duration
                                (e.g. 1s, 10m, 2h etc.). A value of 0 (the default) disables polling.
      --allow-version-mismatch  Allow client and cluster versions mismatch.
+	 --client                  Display the client version only.
+ }
 
 Description:
   Display the version of <BINARY_NAME>.
@@ -86,6 +88,10 @@ Description:
 	fmt.Println("Client Version:   ", VERSION)
 	fmt.Println("Git commit:       ", GIT_REVISION)
 
+	if clientOnly := argutils.ArgBoolOrFalse(parsedArgs, "--client"); clientOnly {
+		return nil
+	}
+
 	// Load the client config and connect.
 	cf := parsedArgs["--config"].(string)
 	client, err := clientmgr.NewClient(cf)