has_feature : template

for plugin-rbd-sheepdog-nexenta

+ indentation fix

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
rbd : rework pool - username - auth_supported options

pool is now optional, default value is 'rbd';
username is now optional, default value is 'admin';

auth_supported option is removed and is autodetected.
  auth = cephx if private key exist
  auth = none if private key does not exist

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>