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.
vdc-manage: refactor backup_object common options.
vdc-manage: takes out default from host subcommand common opts.
vdc-manage: takes out default from storage subcommand common opts.
vdc-manage: takes out default from network subcommand common opts.
vdc-manage: refactor resource_group common options.
Merge pull request #469 from axsh/fix-cli-params

Fix unexpected field value changing for "vdc-manage host modify" and "vdc-manage storage modify"