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
diff --git a/tempest/lib/api_schema/response/volume/hosts.py b/tempest/lib/api_schema/response/volume/hosts.py
index d4848d5..ce67e9f 100644
--- a/tempest/lib/api_schema/response/volume/hosts.py
+++ b/tempest/lib/api_schema/response/volume/hosts.py
@@ -31,7 +31,7 @@
                                 'total_volume_gb': {'type': 'string'},
                                 'total_snapshot_gb': {'type': 'string'},
                                 'project': {'type': 'string'},
-                                'host': {'type': 'string', 'pattern': '.+@.+'},
+                                'host': {'type': 'string'},
                                 'snapshot_count': {'type': 'string'},
                             },
                             'additionalProperties': False,