xenops: dm-agent: add drive device

For QEMU upstrream we use command line to pass drive instead of
XenStore.
dmagent: pass to stubdom cmdline a flag for qemu-dm
[xenops-dmagent] handle cdrom-pt-ro-exclusive
[dmagent] pass to dm-agent a name for nic device
qemu-1.4: add xenmou device configuration for dm-agent

ensure that we use xenmou device with qemu-dm
(not compatible with ioemu)
qemu-1.4: add pci-passthrough information for dm-agent
qemu-1.4: add xenbattery information for dm-agent
[dmagent] drive: move the file name to /dev/xvd(i) instead of /dev/hd(i)
qemu-1.4: allow e1000 net device for qemu by using a config file in /config/e1000
[dmagent] Use ISO images from dom0

Do not skip them entirely so we can pass an ISO even without stubdoms.