qom: Add user_creatable_add_from_str()

This is a version of user_creatable_process_cmdline() with an Error
parameter that never calls exit() and is therefore usable in HMP.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
2 files changed