vdc-manage: fix "host modify" options not to overwrite with default values.
vdc-manage: fix "nfs/iscsistorage modify" not to overwite with default values.
Patch Thor class to allow overwrite method_option attribute.
vdc-manage: refactor network common options.
vdc-manage: refactor backup_storage common options.
vdc-manage: refactor keypair common options.
vdc-manage: refactor security_group common options.