xl: fix the 'upgrade' of Ide devices to Xen devices

Without this patch a VM.start will hang in 'wait_for_plug' because
the hotplug script writes the xvda paths (51712) while xenopsd
waits for the hda paths (768)

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
CA-149017: libxl will reject 4MiB videoram with upstream qemu

If the user asks for 4MiB (-- which is the xapi default, see
[xapi-project/xen-api#1989]) then, if xenopsd is using upstream
qemu, then it will emit a warning and transparently increase the
amount of videoram to the minimum (i.e. 8MiB)

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #142 from djs55/CA-149193

xl: fix the 'upgrade' of Ide devices to Xen devices
Merge pull request #143 from djs55/CA-149017

CA-149017: libxl will reject 4MiB videoram with upstream qemu