Update source to "." to export the octavia openrc

just like the ". /etc/kolla/admin-openrc.sh" [1]

[1]: https://github.com/openstack/kolla-ansible/blob/master/doc/source/user/quickstart.rst

Change-Id: I9c288f31c36654f2ec49e6b3b0fcfc1178e4ad90

doc/source/reference/networking/octavia.rst

@@ -220,7 +220,7 @@ as follows:
 
 .. code-block:: console
 
-   source /etc/kolla/octavia-openrc.sh
+   . /etc/kolla/octavia-openrc.sh
 
 .. note::
 
@@ -353,7 +353,7 @@ Source octavia user openrc:
 
 .. code-block:: console
 
-   source /etc/kolla/octavia-openrc.sh
+   . /etc/kolla/octavia-openrc.sh
 
 .. note::