correct logical error on removing mdraid member role rockstor#1294

Previously we only alterred the mdraid member flag to a disks role
when it's fstype, as reported by scan_disks, indicated the need.
However this was done within a conditional that precluded
examining a 'None' fstype which is what scan_disks translates an
empty string into. Hence we never updated a role db entry for a
previous mdraid member once that member no longer returned an
fstype. Resolved by moving the role label logic outside the
previous conditional such that it now applies to all disks even if
they return no fstype from scan_disks.
Also added debug logging to help test this new arrangement.

src/rockstor/storageadmin/views/disk.py

@@ -122,21 +122,23 @@ def _update_disk_state():
                 dob.parted = True  # overload use of parted as non btrfs flag.
                 # N.B. this overload use may become redundant with the addition
                 # of the Disk.role field.
-                if d.fstype == 'isw_raid_member' \
-                        or d.fstype == 'linux_raid_member':
-                    # transfer fstype raid member indicator to role field
-                    dob.role = d.fstype
-                else:
-                    # No identified role from scan_disks() fstype indicator so
-                    # set as None to update db of new drive role. If we don't
-                    # do this then the same drive when re-deployed will inherit
-                    # it's previous role in the db which may be desired but in
-                    # the case of these raid member indicators from scan_disks()
-                    # we have the current truth provided.
-                    # N.B. this if else could be expanded to accommodate other
-                    # roles based on the fs found and also take heed of an
-                    # existing devices db role entry prior to overwriting.
-                    dob.role = None
+            if d.fstype == 'isw_raid_member' or d.fstype == 'linux_raid_member':
+                # transfer fstype raid member indicator to role field
+                dob.role = d.fstype
+                logger.debug('setting db role for %s', dob.name)
+                logger.debug('to role = %s', dob.role)
+            else:
+                # No identified role from scan_disks() fstype indicator so
+                # set as None to update db of new drive role. If we don't
+                # do this then the same drive when re-deployed will inherit
+                # it's previous role in the db which may be desired but in
+                # the case of these raid member indicators from scan_disks()
+                # we have the current truth provided.
+                # N.B. this if else could be expanded to accommodate other
+                # roles based on the fs found and also take heed of an
+                # existing devices db role entry prior to overwriting.
+                dob.role = None
+                logger.debug('setting db role to None for %s', dob.name)
             # If our existing Pool db knows of this disk's pool via it's label:
             if (Pool.objects.filter(name=d.label).exists()):
                 # update the disk db object's pool field accordingly.