Incorrect attachment reported if stale mountpoints exist on instance

[Simon O'Donovan]

When performing multiple volume attach & detach's with an instance. If the attached volume is not unmounted before attachment the mount will remain but will be stale (i.e. the device is no longer listed in "lsblk" but the mount is still present in "/etc/mtab"). Subsequent attaches will show a discrepancy between reported attached device path in cinder & actual device path in the instance.

Steps to recreate:
-Create an instance.
-Create a volume.
-Attach the volume to the instance. (openstack server add volume <instance> <volume> --device /dev/vdb)
-Attached volume will appear as device /dev/vdb on the instance. (lsblk)
-Mount the device (/dev/vdb) to a directory on the instance. (sudo mount <device> <directory>)
-Detach the volume from the instance without unmounting. This will leave a stale mount in "/etc/mtab". (openstack server remove volume <instance> <volume>)
-Attach volume again providing the same path. (openstack server add volume <instance> <volume> --device /dev/vdb)
-Cinder will report the volume attachment path as /dev/vdb whereas the device path on the instance will appear as /dev/vdc/.

[Simon O'Donovan (odonos12)]

The duplicate that this was assigned to has been marked as Invalid and not a Nova bug. See https://bugs.launchpad.net/horizon/+bug/1018253/comments/9 for details. Removing linked duplicate bug so this can be looked at again.