Ensure flushing of IO prior to removing FC device

This patch flushes IO for each SCSI device that
brick removes from the system.  The patch also
flushes a multipath device prior to removing
each underlying LUN associated with the
multipath device.   We were seeing kernel
IO errors in the syslog without calling flush
on the block device, during a detach for a
multipath FibreChannel copy image to volume
action.

Change-Id: I2fae3dccd4fcab22c8f59dcd297581ee9577b779
Closes-Bug: 1318950
(cherry picked from commit 383f460d6d0431d3dbaf32edb7fcb68c25ff1929)
Merge "Ensure flushing of IO prior to removing FC device" into stable/icehouse