NFS backend initialisation fails because immutable directory exists

[Uwe Grawert]

Using a DELL Data Domain storage as NFS backend for cinder-backup, is causing problems for cinder-volume when starting cinder-volume. The storage is creating a `.snapshot` directory in every share. This directory is immutable. cinder-volume is trying to set ownership on the immutable directory:

```
++ cat /run_command
+ CMD='cinder-volume --config-file /etc/cinder/cinder.conf'
+ ARGS=
+ [[ ! -n '' ]]
+ . kolla_extend_start
++ [[ ! -d /var/log/kolla/cinder ]]
+++ stat -c %a /var/log/kolla/cinder
++ [[ 2755 != \7\5\5 ]]
++ chmod 755 /var/log/kolla/cinder
++ . /usr/local/bin/kolla_cinder_extend_start
++++ stat -c %U:%G /var/lib/cinder
+++ [[ cinder:cinder != \c\i\n\d\e\r\:\k\o\l\l\a ]]
+++ sudo chown -R cinder:kolla /var/lib/cinder
chown: changing ownership of '/var/lib/cinder/backup/9f7bf8f32bb0b28394bd9ce0d841b6d9/.snapshot': Remote I/O error
```

```
ERROR:__main__:Failed to change ownership of /var/lib/cinder/backup/9f7bf8f32bb0b28394bd9ce0d841b6d9/.snapshot to 42407:42407
Traceback (most recent call last):
  File "/usr/local/bin/kolla_set_configs", line 345, in set_perms
    os.chown(path, uid, gid)
OSError: [Errno 121] Remote I/O error: '/var/lib/cinder/backup/9f7bf8f32bb0b28394bd9ce0d841b6d9/.snapshot'
```

[Sofia Enriquez (lsofia-enriquez)]

Greetings Uwe Grawert
Looks like this is a configuration problem regarding the DELL Data Domain setup. Please check the Kolla setup.
Thanks in advance
Sofia