In order to access VMware ESX efficiently, we need to send a session
cookie.  This patch is very simple and just allows you to send that
session cookie.  It punts on the question of how you get the session
cookie in the first place, but in practice you can just run a `curl'
command against the server and extract the cookie that way.

To use it, add file.cookie to the curl URL.  For example:

$ qemu-img info 'json: {
    "file.driver":"https",
    "file.url":"https://vcenter/folder/Windows%202003/Windows%202003-flat.vmdk?dcPath=Datacenter&dsName=datastore1",
    "file.sslverify":"off",
    "file.cookie":"vmware_soap_session=\"52a01262-bf93-ccce-d379-8dabb3e55560\""}'
image: [...]
file format: raw
virtual size: 8.0G (8589934592 bytes)
disk size: unavailable
Signed-off-by: NRichard W.M. Jones <rjones@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>