Fix wrong behavior of parsing plugin service name

When the service name end with keyword "os", like: antiddos,
the parsing logic isn't suitable, that cause the service api
version specified by users don't work.

Change-Id: I5d6217c77d7cd2d2f360d78d8561261398b96685
Closes-Bug: #1658614

Author: kiwik

openstackclient/shell.py

@@ -76,7 +76,9 @@ def _load_plugins(self):
         # Loop through extensions to get API versions
         for mod in clientmanager.PLUGIN_MODULES:
             default_version = getattr(mod, 'DEFAULT_API_VERSION', None)
-            option = mod.API_VERSION_OPTION.replace('os_', '')
+            # Only replace the first instance of "os", some service names will
+            # have "os" in their name, like: "antiddos"
+            option = mod.API_VERSION_OPTION.replace('os_', '', 1)
             version_opt = str(self.cloud.config.get(option, default_version))
             if version_opt:
                 api = mod.API_NAME

releasenotes/notes/bug-1658614-f84a8cece6f2ef8c.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fix wrong behavior of parsing plugin service name when the service name end
+    with keyword ``os``, like: antiddos. That cause the service api version
+    specified by users don't work.
+    [Bug `1658614 <https://bugs.launchpad.net/python-openstackclient/+bug/1658614>`_]