rng: initialize file descriptor to -1

The file descriptor is never initialized to -1, which makes rng-random
close stdin if an object is created and immediately destroyed.  If we
change it to -1, we also need to protect qemu_set_fd_handler from
receiving a bogus file descriptor.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
monitor: add object-add (QMP) and object_add (HMP) command

Add two commands that are the monitor counterparts of -object.  The commands
have the same Visitor-based implementation, but use different kinds of
visitors so that the HMP command has a DWIM string-based syntax, while
the QMP variant accepts a stricter JSON-based properties dictionary.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
monitor: add object-del (QMP) and object_del (HMP) command

These two commands invoke the "unparent" method of Object.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
mtree: remove write-only field

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>