Fix "Error: Device 51952 not connected" error when using pygrub

Fix "Error: Device 51952 not connected" error when using pygrub

The following is the process of booting a DomU with 'mounted-blktap2' (VHD
for example) and 'pygrub' as bootloader:

1. Connect boot-device to Dom0 as '/dev/xpvd'
2. Pygrub get info for load DomU
3. Disconnect boot-device from Dom0
4. Boot DomU

During step 3 the created device is disconnected from Dom0, but
xenstore does not scrape away after the device is disconnected so you
get the following error:

    "Error: Device /dev/xvdp (51952, tap2) is already connected."

During step 3 xend calls destroyDevice always with 'tap' as argument.

Signed-off-by: eXeC001er <execooler@gmail.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
committer: Stefano Stabellini <stefano.stabellini@eu.citrix.com>