qemu-storage-daemon: Add barebone tool

This adds a new binary qemu-storage-daemon that doesn't yet do more than
some typical initialisation for tools and parsing the basic command
options --version, --help and --trace.

Even though this doesn't add any options yet that create things (like
--object or --blockdev), already document that we're planning to process
them in the order they are given on the command line rather than trying
(and failing, like vl.c) to resolve dependencies between options
automatically.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200224143008.13362-2-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>