Fix config parse when caller has args

When the Python script using cinderlib had arguments we would get an
Oslo Config usage error when initializing cinderlib.

This was caused by the _CachedArgumentParser class parsing argv, so we
replace this parsing with NOOP.

HISTORY.rst

@@ -2,6 +2,13 @@
 History
 =======
 
+0.3.x (2019-01-xx)
+------------------
+
+- Bug fixes:
+
+  - Failure when the caller has arguments
+
 0.3.1 (2019-01-16)
 ------------------
 

cinderlib/cinderlib.py

@@ -220,6 +220,9 @@ class Backend(object):
         cfg.ConfigParser.parse = six.create_unbound_method(cls._config_parse,
                                                            cfg.ConfigParser)
 
+        # Replace command line arg parser so we ignore caller's args
+        cfg._CachedArgumentParser.parse_args = lambda *a, **kw: None
+
         # Update the configuration with the options we have configured
         cfg.CONF(project='cinder', version=cinderlib.__version__,
                  default_config_files=['in_memory_file'])