virttest.qemu_vm: Do not check cdrom available when gluster used.

Signed-off-by: Feng Yang <fyang@redhat.com>
shared.cfg: Update gluster config.

Signed-off-by: Feng Yang <fyang@redhat.com>
virttest.storage: Only generate image path when image_name set.

This patch make not_insert_at_start works  for cdrom device.
We support not_insert_at_start parameter by unset image_name parameter.

Signed-off-by: Feng Yang <fyang@redhat.com>
Merge pull request #1930 from FengYang/gluster

Gluster