bin: add the parameter disabling HTTP bootstrapping

Particularly useful together with locally stored metadata.

I am not sure how to get rid of the need to need to provide URL
when I just want to let pyodata parse locally stored metadata.

The newly introduced option will allow me to run pyodata with
dummy URL because no request HTTP request will be send.

If you find a better User Experience, feel free to rework it.

Usage:
  pyodata DUMMY_FAKE_URL --no-session-init --metdata ./metadata.xml

bin/pyodata

@@ -67,6 +67,8 @@ def _parse_args(argv):
     parser.add_argument('--password', default=None, type=str)
     parser.add_argument('--metadata', default=None, type=str,
                         help='Path to the XML file with service $metadata')
+    parser.add_argument('--no-session-init', default=False,
+                        action='store_true', help='Skip HTTP session initialization')
     parser.set_defaults(func=print_out_metadata_info)
 
     subparsers = parser.add_subparsers()
@@ -97,13 +99,17 @@ def _main(argv):
 
         session.auth = (args.user, args.password)
 
-    try:
-        session.head(args.SERVICE_ROOT_URL)
-        args.password = 'xxxxx'
-    except pyodata.exceptions.HttpError as err:
-        sys.stderr.write(str(err))
-        sys.stderr.write('\n')
-        sys.exit(1)
+    # Oh, I am sorry for the double negation,
+    # but I cannot find a better construction.
+    if not args.no_session_init:
+        print('[Initializing HTTP session ...]')
+        try:
+            session.head(args.SERVICE_ROOT_URL)
+            args.password = 'xxxxx'
+        except pyodata.exceptions.HttpError as err:
+            sys.stderr.write(str(err))
+            sys.stderr.write('\n')
+            sys.exit(1)
 
     static_metadata = None
     if args.metadata: