saveconfig: way for block-level save with delete command
saveconfig: way for block-level save with delete command

currently, we can use block-level save feature for create command and
reconfig of different attributes, but there is no way to use block-level
feature for delete command.

This patch introduces 'save' flag (False on default), which can trigger
saveconfig internally as part of delete command.

$ targetcli /backstores/user:glfs delete test save=True
Deleted storage object test.

Signed-off-by: Prasanna Kumar Kalever <a78d8f98557446023f5b3ba9944d7be259a978a3@redhat.com>

agrover/targetcli-fb,cvubrugier/targetcli-fb