Add generic to create secret command

The generic is missing from the command and will cause error: `Error: unknown flag: --type` when running the command.

Author: xcompass

docs/user-guide/persistent-volumes/index.md

@@ -423,7 +423,7 @@ parameters:
 * `restuserkey` : Gluster REST service/Heketi user's password which will be used for authentication to the REST server. This parameter is deprecated in favor of `secretNamespace` + `secretName`.
 * `secretNamespace` + `secretName` : Identification of Secret instance that containes user password to use when talking to Gluster REST service. These parameters are optional, empty password will be used when both `secretNamespace` and `secretName` are omitted. The provided secret must have type "kubernetes.io/glusterfs", e.g. created in this way:
   ```
-  $ kubectl create secret heketi-secret --type="kubernetes.io/glusterfs" --from-literal=key='opensesame' --namespace=default
+  $ kubectl create secret generic heketi-secret --type="kubernetes.io/glusterfs" --from-literal=key='opensesame' --namespace=default
   ```
 
 #### OpenStack Cinder
@@ -482,7 +482,7 @@ parameters:
 * `userId`: Ceph client ID that is used to map the RBD image. Default is the same as `adminId`.
 * `userSecretName`: The name of Ceph Secret for `userId` to map RBD image. It must exist in the same namespace as PVCs. This parameter is required. The provided secret must have type "kubernetes.io/rbd", e.g. created in this way:
   ```
-  $ kubectl create secret ceph-secret --type="kubernetes.io/rbd" --from-literal=key='QVFEQ1pMdFhPUnQrSmhBQUFYaERWNHJsZ3BsMmNjcDR6RFZST0E9PQ==' --namespace=kube-system
+  $ kubectl create secret generic ceph-secret --type="kubernetes.io/rbd" --from-literal=key='QVFEQ1pMdFhPUnQrSmhBQUFYaERWNHJsZ3BsMmNjcDR6RFZST0E9PQ==' --namespace=kube-system
   ```
 
 #### Quobyte
@@ -509,7 +509,7 @@ parameters:
 * `adminSecretNamespace`: The namespace for `adminSecretName`. Default is "default".
 * `adminSecretName`: secret that holds information about the Quobyte user and the password to authenticate agains the API server. The provided secret must have type "kubernetes.io/quobyte", e.g. created in this way:
   ```
-  $ kubectl create secret quobyte-admin-secret --type="kubernetes.io/quobyte" --from-literal=key='opensesame' --namespace=kube-system
+  $ kubectl create secret generic quobyte-admin-secret --type="kubernetes.io/quobyte" --from-literal=key='opensesame' --namespace=kube-system
   ```
 * `user`: maps all access to this user. Default is "root".
 * `group`: maps all access to this group. Default is "nfsnobody".