qemu-storage-daemon: Remove QemuOpts from --object parser

The command line parser for --object parses the input twice: Once into
QemuOpts just for detecting help options, and then again into a QDict
using the keyval parser for actually creating the object.

Now that the keyval parser can also detect help options, we can simplify
this and remove the QemuOpts part.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20201007164903.282198-5-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>