support long nutanix device names

[phillxnet]

Thanks to forum member @dannyboy1121 it has come to light that serial numbers of Nutanix CE block devices (a KVM based platform) can exceed that of Rockstor's Disk.name db field, assuming the consequent by-id name uses the entire serial number. Is is not yet know however if udev is even providing the require by-id names. A request in the following forum thread has been placed to gain further information on the /dev/disk/by-id mappings that are required for all Rockstor versions from 3.8-14.02 onwards.

Please update the following forum thread for significant progress on this issue:
https://forum.rockstor.com/t/adding-virtual-disks-pool-issues/2006

[phillxnet]

@dannyboy1121 has responded in the referenced forum thread with an ls -la of /dev/disk/by-id which showed that by-id mappings were present and the base device names were of the form:
"scsi-1NUTANIX_NFS_3_0_453_" = 26 chars and then a uuid reference
of the usual 8_4_4_4_12 = 36 chars format, so the total length is 62 chars.
This is OK for the existing Disk.name db field however the system disk name would add an additional:
"-part3" = 6 chars to address the partition component of the by-id name.

So the end result is a failure to accommodate the system disk by-id name of 68 chars.

I propose that we double the current 64 char Disk.name db field to 128 chars; especially in light of potentially accommodating iSCSI targets which may likewise have very long by-id name references.

[phillxnet]

@schakrava I will attempt to prepare a pr for this issue tomorrow (UK) in the hope of making it available ready for the next (pending) stable release. I have seen no other candidates for by-id name overflow and haven't noticed any reports of the same on the forum, for our current testing channel; however these more exotic mappings are the most likely to trigger this limitation, especially given their use of the long uuid4 components.

[phillxnet]

After applying the Disk.name field length changes in:
phillxnet@b038d9f
the following command was run to generated the South db migration file:

[root@rockdev rockstor-dev]# /opt/rockstor-dev/bin/django schemamigration storageadmin --auto
 ~ Changed field name on storageadmin.Disk
Created 0047_auto__chg_field_disk_name.py. You can now apply this migration with: ./manage.py migrate storageadmin

[phillxnet]

From local db access prior to migration command we have:

\d storageadmin_disk;

   Column      |          Type           |                           Modifiers
...
name            | character varying(64)   | not null
...

then after a migration command:

[root@rockdev rockstor-dev]# /opt/rockstor-dev/bin/django migrate storageadmin --database=default
Running migrations for storageadmin:
 - Migrating forwards to 0047_auto__chg_field_disk_name.
 > storageadmin:0047_auto__chg_field_disk_name
 - Loading initial data for storageadmin.
Installed 0 object(s) from 0 fixture(s)

we have:

     Column      |          Type           |                           Modifiers
...
name            | character varying(128)  | not null
...