qemu-img: allow specifying image as a set of options args

Currently qemu-img allows an image filename to be passed on the
command line, but unless using the JSON format, it does not have
a way to set any options except the format eg

   qemu-img info https://127.0.0.1/images/centos7.iso

This adds a --image-opts arg that indicates that the positional
filename should be interpreted as a full option string, not
just a filename.

   qemu-img info --image-opts driver=https,url=https://127.0.0.1/images,sslverify=off



This flag is mutually exclusive with the '-f' / '-F' flags.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>