Default enable --stream by default

Now that we've switched to centos-stream by default it
should be the defualt when tripleo-repos is run.

Change-Id: I4581479df6e69b0f3d233636ee71d028344d230a

releasenotes/notes/stream_by_default-783cc6a2208b942c.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    tripleo-repos now runs with the --stream argument enabled by default. Use
+    the --no-stream argument when using tripleo-repos without CentOS stream.

tripleo_repos/main.py

@@ -199,7 +199,7 @@ def _parse_args(distro_id, distro_major_version_id):
     stream_group = parser.add_mutually_exclusive_group()
     stream_group.add_argument('--stream',
                               action='store_true',
-                              default=False,
+                              default=True,
                               help='Enable stream support for CentOS repos')
     stream_group.add_argument('--no-stream',
                               action='store_true',