kubernetes-csi-addons test: Add testing tool for VolumeGroup

This commit adds testing tool for VolumeGroup operations such as-

CreateVolumeGroup
ModifyVolumeGroup Membership
DeleteVolumeGroup
ControllerGetVolumeGroup

Resolves #653

Sample outputs for the cli commands of the form: kubectl exec -c csi-addons <csi-addons-nodeplugin> -n rook-ceph -- csi-addons -operation <operationName> -secret <namespace/name> -parameters <key1=value1,...>

CreateVolumeGroup: Volume Group created: volume_group:{volume_group_id:"0001-0009-rook-ceph-0000000000000002-21fb957f-7987-44f8-972c-36c6e57896b0"}
ModifyVolumeGroupMembership: Volume Group Membership modified for- volume_group:{volume_group_id:"0001-0009-rook-ceph-0000000000000002-21fb957f-7987-44f8-972c-36c6e57896b0"}
DeleteVolumeGroup: Volume Group Deleted.
ControllerGetVolumeGroup: Controller Volume Group Info: volume_group:{volume_group_id:"0001-0009-rook-ceph-0000000000000002-21fb957f-7987-44f8-972c-36c6e578"}