CA-283724: Don't attach CBT log when VDI attached in RO mode
CA-283724: Don't attach CBT log when VDI attached in RO mode

Attaching a VDI with its CBT log marks the latter dirty. When this happens
simultaneously on two different hosts, the second hosts marks the CBT
content incosistent and disables CBT on the disk. This can be avoided if
the disks are only being attached in RO mode.

Signed-off-by: Chandrika Srinivasan <51ae5eeda27fe08017d2d63c87755f0707891830@citrix.com>
Reviewed-by: Mark Syms <655512b2a8f1aba6e4085462b623575da824f038@citrix.com>

xapi-project/sm,xapi-project/sm,chandrikas/sm,chandrikas/sm,chandrikas/sm,xapi-project/sm