Fix volume host schema: host name may not contain '@'

Host name in the response of show-host may not contain '@',
which makes https://review.opendev.org/#/c/678998/ fail.
This is to remove the strict check of '@', and the cinder
api-ref patch is https://review.opendev.org/#/c/679883/

Change-Id: I2c9339528eeb3bea3474709b261deec27d16d0b8
partially-implements: blueprint volume-response-schema-validation
1 file changed