Enhance secondary node replace for drbd8

Enhance secondary node replace for drbd8

This (big) patch does two things:
  - add "local disk status" to the block device checks
    (BlockDevice.GetSyncStatus and the rpc calls that call this
    function, and therefore cmdlib._CheckDiskConsistency)
  - improve the drbd8 secondary replace operation using the above
    functionality

The "local disk status" adds a new variable to the result of
GetSyncStatus that shows the degradation of the local storage of the
device. Of course, not all device support this - for now, we only modify
LogicalVolumes and DRBD8 to return degraded in some cases, other devices
always return non-degraded. This variable should be a subset of
is_degraded - whenever this variable is true, the is_degraded should
also be true.

The drbd8 secondary replace uses this variable as we don't care if the
primary drbd device is network-degraded, only if it has good local disk
data (ldisk is False).

The patch also increases the protocol version (due to rpc changes).

Reviewed-by: imsnah