Added code to support qliksense way to do preflight checks (#5)

* Added code to support qliksense way to do preflight checks

README.md

@@ -9,6 +9,13 @@ Download the appropriate executable for your platform from the [releases page](h
 To make sure everything is order, you can fetch the Qlik Sense bundle version and corresponding image list from:
  - `qliksense about --tag qlik/qliksense-cnab-bundle:latest `
 
+## Running Preflight checks
+You can run preflight checks to ensure that the cluster is in a healthy state before installing Qliksense. 
+- `qliksense preflight -c <credential_name> `
+
+The above command runs the checks in the default namespace. If you want to specify the namespace to run preflight checks on:
+- `qliksense preflight --param namespace=<value> -c <credential_name> `
+
 ## Qliksense Packaging
 Packaging of Qlik Sense on Kubernetes is done through a [Porter](https://porter.sh/) definition in the [Qlik Sense on Kubernetes configuration repository](https://github.com/qlik-oss/qliksense-k8s/blob/master/porter.yaml), the resulting bundle published on DockerHub as a [Cloud Natvie Application Bundle](https://cnab.io/) called [qliksense-cnab-bundle](https://hub.docker.com/r/qlik/qliksense-cnab-bundle).
 ### Versioning

cmd/qliksense/aliases.go

@@ -15,6 +15,7 @@ func buildAliasCommands(porterCmd *cobra.Command, q *qliksense.Qliksense) []*cob
 		buildBuildAlias(porterCmd),
 		buildInstallAlias(porterCmd, q),
 		buildAboutAlias(porterCmd),
+		buildPreflightAlias(porterCmd, q),
 	}
 
 }
@@ -172,6 +173,36 @@ func buildAboutAlias(porterCmd *cobra.Command) *cobra.Command {
 	return c
 }
 
+func buildPreflightAlias(porterCmd *cobra.Command, q *qliksense.Qliksense) *cobra.Command {
+	var (
+		c    *cobra.Command
+		opts *paramOptions
+	)
+
+	opts = &paramOptions{}
+
+	c = &cobra.Command{
+		Use:   "preflight",
+		Short: "Preflight Checks",
+		Long:  "Perform Preflight Checks",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			args = append(os.Args[1:], opts.getTagDefaults(args)...)
+			return porterCmd.RunE(porterCmd, append([]string{"invoke", "--action", "preflight"}, args...))
+		},
+		Annotations: map[string]string{
+			"group": "alias",
+		},
+	}
+	f := c.Flags()
+	f.StringSliceVar(&opts.Params, "param", nil,
+		"Define an individual parameter in the form NAME=VALUE. Overrides parameters set with the same name using --param-file. May be specified multiple times.")
+	f.StringSliceVar(&opts.ParamFiles, "param-file", nil,
+		"Path to a parameters definition file for the bundle, each line in the form of NAME=VALUE. May be specified multiple times.")
+	f.StringSliceVarP(&opts.CredentialIdentifiers, "cred", "c", nil,
+		"Credential to use when installing the bundle. May be either a named set of credentials or a filepath, and specified multiple times.")
+	return c
+}
+
 func (o *paramOptions) findKey(param string) *string {
 	var (
 		value *string