memcache: Remove "default" username and password

Because these are not intentional default. This also adds a validation
logic to catch the case where SASL is requested but username or
password is not given.

Change-Id: Ia98bfc5f9a42c13acfdb2192bb1fa11773f6ccf8

oslo_cache/_opts.py

@@ -122,10 +122,8 @@ FILE_OPTIONS = {
                     help='Enable the SASL(Simple Authentication and Security'
                          'Layer) if the SASL_enable is true, else disable.'),
         cfg.StrOpt('memcache_username',
-                   default='',
                    help='the user name for the memcached which SASL enabled'),
         cfg.StrOpt('memcache_password',
-                   default='',
                    secret=True,
                    help='the password for the memcached which SASL enabled'),
         cfg.BoolOpt('tls_enabled',

oslo_cache/backends/memcache_pool.py

@@ -27,6 +27,7 @@ except ImportError as e:
     else:
         raise
 from oslo_cache import _memcache_pool
+from oslo_cache import exception
 
 
 # Helper to ease backend refactoring
@@ -63,6 +64,11 @@ class PooledMemcachedBackend(memcached_backend.MemcachedBackend):
     def __init__(self, arguments):
         super(PooledMemcachedBackend, self).__init__(arguments)
         if arguments.get('sasl_enabled', False):
+            if (arguments.get('username') is None or
+                    arguments.get('password') is None):
+                raise exception.ConfigurationError(
+                    'username and password should be configured to use SASL '
+                    'authentication.')
             if not _bmemcache_pool:
                 raise ImportError("python-binary-memcached package is missing")
             self.client_pool = _bmemcache_pool.BMemcacheClientPool(