CA-145685: Create a tap disk to pass the host DVD drive to a PV guest

More robust version. Supersedes commit 050d45de

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>
CA-145685: [UnitTest] Add unit tests

Supersedes commit 801f9e9c

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>
Merge CA-145685 into xs64bit (new version)

Signed-off-by: Germano Percossi <germano.percossi@citrix.com>

GitHub: closes #226 on xapi-project/sm