Fixes incorrect class path in logging_sample.conf

It seems to be a leak in 'Change-Id:
I95d23aafe19b12d4a427149aa5f7a66394d178c6'.

Change-Id: I4c2777049ec9e301a1f05b3a7b4aa5dd71c033e3
Closes-Bug: #1233985

etc/cinder/logging_sample.conf

@@ -5,7 +5,7 @@ keys = root, cinder
 keys = stderr, stdout, watchedfile, syslog, null
 
 [formatters]
-keys = legacycinder, default
+keys = context, default
 
 [logger_root]
 level = WARNING
@@ -47,30 +47,30 @@ qualname = eventlet.wsgi.server
 [handler_stderr]
 class = StreamHandler
 args = (sys.stderr,)
-formatter = legacycinder
+formatter = context
 
 [handler_stdout]
 class = StreamHandler
 args = (sys.stdout,)
-formatter = legacycinder
+formatter = context
 
 [handler_watchedfile]
 class = handlers.WatchedFileHandler
 args = ('cinder.log',)
-formatter = legacycinder
+formatter = context
 
 [handler_syslog]
 class = handlers.SysLogHandler
 args = ('/dev/log', handlers.SysLogHandler.LOG_USER)
-formatter = legacycinder
+formatter = context
 
 [handler_null]
 class = cinder.openstack.common.log.NullHandler
 formatter = default
 args = ()
 
-[formatter_legacycinder]
-class = cinder.openstack.common.log.LegacyFormatter
+[formatter_context]
+class = cinder.openstack.common.log.ContextFormatter
 
 [formatter_default]
 format = %(message)s