Add --client flag to pgo version to return only pgo client version

This skips making a call to the API server so the user can know the
version of the pgo client that they are using. This mimics the kubectl
functionality, i.e. `kubectl version --client`.

Issue: #1600

Author: jkatz

docs/content/pgo-client/reference/pgo_version.md

@@ -18,7 +18,8 @@ pgo version [flags]
 ### Options
 
 ```
-  -h, --help   help for version
+      --client   Only return the version of the pgo client. This does not make a call to the API server.
+  -h, --help     help for version
 ```
 
 ### Options inherited from parent commands
@@ -38,4 +39,4 @@ pgo version [flags]
 
 * [pgo](/pgo-client/reference/pgo/)	 - The pgo command line interface.
 
-###### Auto generated by spf13/cobra on 31-Dec-2019
+###### Auto generated by spf13/cobra on 4-Jun-2020

pgo/cmd/version.go

@@ -24,6 +24,10 @@ import (
 	"os"
 )
 
+// ClientVersionOnly indicates that only the client version should be returned, not make
+// a call to the server
+var ClientVersionOnly bool
+
 var versionCmd = &cobra.Command{
 	Use:   "version",
 	Short: "Print version information for the PostgreSQL Operator",
@@ -38,24 +42,31 @@ var versionCmd = &cobra.Command{
 
 func init() {
 	RootCmd.AddCommand(versionCmd)
+	versionCmd.Flags().BoolVar(&ClientVersionOnly, "client", false, "Only return the version of the pgo client. This does not make a call to the API server.")
 }
 
 func showVersion() {
 
+	// print the client version
+	fmt.Println("pgo client version " + msgs.PGO_VERSION)
+
+	// if the user selects only to display the client version, return here
+	if ClientVersionOnly {
+		return
+	}
+
+	// otherwise, get the server version
 	response, err := api.ShowVersion(httpclient, &SessionCredentials)
 
 	if err != nil {
 		fmt.Println("Error: " + err.Error())
 		os.Exit(2)
 	}
 
-	fmt.Println("pgo client version " + msgs.PGO_VERSION)
-
-	if response.Status.Code == msgs.Ok {
-		fmt.Println("pgo-apiserver version " + response.Version)
-	} else {
+	if response.Status.Code != msgs.Ok {
 		fmt.Println("Error: " + response.Status.Msg)
-		os.Exit(2)
+		os.Exit(1)
 	}
 
+	fmt.Println("pgo-apiserver version " + response.Version)
 }